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 $95.94   8.120%   $103.7303   $103.73   $103.75   $103.70  
  Purchase #2 $249.61   9.475%   $273.2605   $273.26   $273.25   $273.30  
  Purchase #3 $82.58   6.203%   $87.7024   $87.70   $87.70   $87.70  
  Purchase #4 $211.73   13.501%   $240.3157   $240.32   $240.30   $240.30  
  Purchase #5 $96.81   5.790%   $102.4153   $102.42   $102.40   $102.40  
  Purchase #6 $58.52   10.211%   $64.4955   $64.50   $64.50   $64.50  
  Purchase #7 $132.71   13.155%   $150.168   $150.17   $150.15   $150.20  
  7 purchase totals = $927.90       $1,022.0877   $1,022.10   $1,022.05   $1,022.10