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 $40.60   7.352%   $43.5849   $43.58   $43.60   $43.60  
  Purchase #2 $235.72   8.122%   $254.8652   $254.87   $254.85   $254.90  
  Purchase #3 $25.86   12.762%   $29.1603   $29.16   $29.15   $29.20  
  Purchase #4 $168.64   10.355%   $186.1027   $186.10   $186.10   $186.10  
  Purchase #5 $153.74   12.746%   $173.3357   $173.34   $173.35   $173.30  
  Purchase #6 $244.49   12.169%   $274.242   $274.24   $274.25   $274.20  
  Purchase #7 $216.47   9.723%   $237.5174   $237.52   $237.50   $237.50  
  7 purchase totals = $1,085.52       $1,198.8082   $1,198.81   $1,198.80   $1,198.80