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 $64.47   11.681%   $72.0007   $72.00   $72.00   $72.00  
  Purchase #2 $111.91   6.354%   $119.0208   $119.02   $119.00   $119.00  
  Purchase #3 $116.98   12.777%   $131.9265   $131.93   $131.95   $131.90  
  Purchase #4 $212.30   6.509%   $226.1186   $226.12   $226.10   $226.10  
  Purchase #5 $96.54   12.119%   $108.2397   $108.24   $108.25   $108.20  
  Purchase #6 $119.39   8.697%   $129.7733   $129.77   $129.75   $129.80  
  Purchase #7 $141.98   5.648%   $149.999   $150.00   $150.00   $150.00  
  7 purchase totals = $863.57       $937.0786   $937.08   $937.05   $937.00