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 $211.52   11.373%   $235.5762   $235.58   $235.60   $235.60  
  Purchase #2 $179.81   7.140%   $192.6484   $192.65   $192.65   $192.60  
  Purchase #3 $188.56   8.571%   $204.7215   $204.72   $204.70   $204.70  
  Purchase #4 $24.93   10.853%   $27.6357   $27.64   $27.65   $27.60  
  Purchase #5 $227.67   13.596%   $258.624   $258.62   $258.60   $258.60  
  Purchase #6 $132.98   3.634%   $137.8125   $137.81   $137.80   $137.80  
  Purchase #7 $193.49   11.617%   $215.9677   $215.97   $215.95   $216.00  
  7 purchase totals = $1,158.96       $1,272.9860   $1,272.99   $1,272.95   $1,272.90