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 $23.95   4.264%   $24.9712   $24.97   $24.95   $25.00  
  Purchase #2 $151.95   11.679%   $169.6962   $169.70   $169.70   $169.70  
  Purchase #3 $10.75   6.153%   $11.4114   $11.41   $11.40   $11.40  
  Purchase #4 $59.65   6.827%   $63.7223   $63.72   $63.70   $63.70  
  Purchase #5 $182.25   4.608%   $190.6481   $190.65   $190.65   $190.60  
  Purchase #6 $193.36   13.601%   $219.6589   $219.66   $219.65   $219.70  
  Purchase #7 $118.31   11.678%   $132.1262   $132.13   $132.15   $132.10  
  7 purchase totals = $740.22       $812.2343   $812.24   $812.20   $812.20