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 $64.82   8.427%   $70.2824   $70.28   $70.30   $70.30  
  Purchase #2 $195.86   5.317%   $206.2739   $206.27   $206.25   $206.30  
  Purchase #3 $203.48   4.459%   $212.5532   $212.55   $212.55   $212.60  
  Purchase #4 $61.68   7.435%   $66.2659   $66.27   $66.25   $66.30  
  Purchase #5 $183.51   10.263%   $202.3436   $202.34   $202.35   $202.30  
  Purchase #6 $11.61   13.463%   $13.1731   $13.17   $13.15   $13.20  
  Purchase #7 $99.27   12.604%   $111.782   $111.78   $111.80   $111.80  
  7 purchase totals = $820.23       $882.6741   $882.66   $882.65   $882.80