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 $64.59   10.613%   $71.4449   $71.44   $71.45   $71.40  
  Purchase #2 $180.69   11.517%   $201.5001   $201.50   $201.50   $201.50  
  Purchase #3 $5.93   7.444%   $6.3714   $6.37   $6.35   $6.40  
  Purchase #4 $132.63   6.432%   $141.1608   $141.16   $141.15   $141.20  
  Purchase #5 $66.31   3.763%   $68.8052   $68.81   $68.80   $68.80  
  Purchase #6 $181.26   10.287%   $199.9062   $199.91   $199.90   $199.90  
  Purchase #7 $244.55   3.761%   $253.7475   $253.75   $253.75   $253.70  
  7 purchase totals = $875.96       $942.9361   $942.94   $942.90   $942.90