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 $138.65   9.613%   $151.9784   $151.98   $152.00   $152.00  
  Purchase #2 $141.43   5.807%   $149.6428   $149.64   $149.65   $149.60  
  Purchase #3 $11.30   3.297%   $11.6726   $11.67   $11.65   $11.70  
  Purchase #4 $88.29   11.120%   $98.1078   $98.11   $98.10   $98.10  
  Purchase #5 $157.96   7.368%   $169.5985   $169.60   $169.60   $169.60  
  Purchase #6 $84.82   9.438%   $92.8253   $92.83   $92.85   $92.80  
  Purchase #7 $213.46   10.730%   $236.3643   $236.36   $236.35   $236.40  
  7 purchase totals = $835.91       $910.1897   $910.19   $910.20   $910.20