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 $132.81   10.636%   $146.9357   $146.94   $146.95   $146.90  
  Purchase #2 $138.56   8.385%   $150.1783   $150.18   $150.20   $150.20  
  Purchase #3 $123.92   9.439%   $135.6168   $135.62   $135.60   $135.60  
  Purchase #4 $139.81   8.633%   $151.8798   $151.88   $151.90   $151.90  
  Purchase #5 $168.61   5.781%   $178.3573   $178.36   $178.35   $178.40  
  Purchase #6 $60.33   4.565%   $63.0841   $63.08   $63.10   $63.10  
  Purchase #7 $151.41   12.845%   $170.8586   $170.86   $170.85   $170.90  
  7 purchase totals = $915.45       $996.9106   $996.92   $996.95   $997.00