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 $48.65   7.513%   $52.3051   $52.31   $52.30   $52.30  
  Purchase #2 $212.51   10.686%   $235.2188   $235.22   $235.20   $235.20  
  Purchase #3 $19.84   4.404%   $20.7138   $20.71   $20.70   $20.70  
  Purchase #4 $70.54   13.803%   $80.2766   $80.28   $80.30   $80.30  
  Purchase #5 $133.40   7.391%   $143.2596   $143.26   $143.25   $143.30  
  Purchase #6 $248.78   9.597%   $272.6554   $272.66   $272.65   $272.70  
  Purchase #7 $21.39   11.370%   $23.822   $23.82   $23.80   $23.80  
  7 purchase totals = $755.11       $828.2513   $828.26   $828.20   $828.30