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 $36.56   13.484%   $41.4898   $41.49   $41.50   $41.50  
  Purchase #2 $223.32   9.501%   $244.5376   $244.54   $244.55   $244.50  
  Purchase #3 $20.27   8.516%   $21.9962   $22.00   $22.00   $22.00  
  Purchase #4 $166.66   5.149%   $175.2413   $175.24   $175.25   $175.20  
  Purchase #5 $146.42   12.573%   $164.8294   $164.83   $164.85   $164.80  
  Purchase #6 $209.64   12.249%   $235.3188   $235.32   $235.30   $235.30  
  Purchase #7 $27.49   13.113%   $31.0948   $31.09   $31.10   $31.10  
  7 purchase totals = $830.36       $914.5079   $914.51   $914.55   $914.40