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 $134.51   12.822%   $151.7569   $151.76   $151.75   $151.80  
  Purchase #2 $113.61   4.121%   $118.2919   $118.29   $118.30   $118.30  
  Purchase #3 $16.89   3.263%   $17.4411   $17.44   $17.45   $17.40  
  Purchase #4 $55.45   3.571%   $57.4301   $57.43   $57.45   $57.40  
  Purchase #5 $215.72   13.162%   $244.1131   $244.11   $244.10   $244.10  
  Purchase #6 $97.34   13.528%   $110.5082   $110.51   $110.50   $110.50  
  Purchase #7 $217.43   7.640%   $234.0417   $234.04   $234.05   $234.00  
  7 purchase totals = $850.95       $933.5830   $933.58   $933.60   $933.50