Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $118.44   12.245%   $132.943   $132.94   $132.95   $132.90  
  Purchase #2 $194.77   9.168%   $212.6265   $212.63   $212.65   $212.60  
  Purchase #3 $246.64   7.306%   $264.6595   $264.66   $264.65   $264.70  
  Purchase #4 $184.44   4.236%   $192.2529   $192.25   $192.25   $192.30  
  Purchase #5 $197.95   12.384%   $222.4641   $222.46   $222.45   $222.50  
  Purchase #6 $109.42   11.631%   $122.1466   $122.15   $122.15   $122.10  
  Purchase #7 $242.30   12.471%   $272.5172   $272.52   $272.50   $272.50  
  7 purchase totals = $1,293.96       $1,419.6098   $1,419.61   $1,419.60   $1,419.60