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 $144.41   5.249%   $151.9901   $151.99   $152.00   $152.00  
  Purchase #2 $222.75   4.600%   $232.9965   $233.00   $233.00   $233.00  
  Purchase #3 $27.83   11.479%   $31.0246   $31.02   $31.00   $31.00  
  Purchase #4 $203.45   10.394%   $224.5966   $224.60   $224.60   $224.60  
  Purchase #5 $120.58   7.749%   $129.9237   $129.92   $129.90   $129.90  
  Purchase #6 $50.78   12.456%   $57.1052   $57.11   $57.10   $57.10  
  Purchase #7 $98.80   8.323%   $107.0231   $107.02   $107.00   $107.00  
  7 purchase totals = $868.60       $934.6598   $934.66   $934.60   $934.60