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 $206.95   13.408%   $234.6979   $234.70   $234.70   $234.70  
  Purchase #2 $83.28   10.754%   $92.2359   $92.24   $92.25   $92.20  
  Purchase #3 $220.30   7.267%   $236.3092   $236.31   $236.30   $236.30  
  Purchase #4 $61.32   3.245%   $63.3098   $63.31   $63.30   $63.30  
  Purchase #5 $139.39   8.209%   $150.8325   $150.83   $150.85   $150.80  
  Purchase #6 $125.43   6.297%   $133.3283   $133.33   $133.35   $133.30  
  Purchase #7 $52.68   11.664%   $58.8246   $58.82   $58.80   $58.80  
  7 purchase totals = $889.35       $969.5382   $969.54   $969.55   $969.40