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 $228.43   8.645%   $248.1778   $248.18   $248.20   $248.20  
  Purchase #2 $76.71   12.437%   $86.2504   $86.25   $86.25   $86.30  
  Purchase #3 $59.95   5.205%   $63.0704   $63.07   $63.05   $63.10  
  Purchase #4 $118.31   4.118%   $123.182   $123.18   $123.20   $123.20  
  Purchase #5 $68.57   9.126%   $74.8277   $74.83   $74.85   $74.80  
  Purchase #6 $127.77   9.671%   $140.1266   $140.13   $140.15   $140.10  
  Purchase #7 $86.92   9.663%   $95.3191   $95.32   $95.30   $95.30  
  7 purchase totals = $766.66       $830.9540   $830.96   $831.00   $831.00