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 $101.62   3.266%   $104.9389   $104.94   $104.95   $104.90  
  Purchase #2 $201.93   11.395%   $224.9399   $224.94   $224.95   $224.90  
  Purchase #3 $212.42   10.635%   $235.0109   $235.01   $235.00   $235.00  
  Purchase #4 $12.38   4.580%   $12.947   $12.95   $12.95   $12.90  
  Purchase #5 $40.32   9.679%   $44.2226   $44.22   $44.20   $44.20  
  Purchase #6 $198.39   3.609%   $205.5499   $205.55   $205.55   $205.50  
  Purchase #7 $227.38   6.602%   $242.3916   $242.39   $242.40   $242.40  
  7 purchase totals = $994.44       $1,070.0008   $1,070.00   $1,070.00   $1,069.80