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 $88.59   8.166%   $95.8243   $95.82   $95.80   $95.80  
  Purchase #2 $34.83   6.111%   $36.9585   $36.96   $36.95   $37.00  
  Purchase #3 $142.94   10.744%   $158.2975   $158.30   $158.30   $158.30  
  Purchase #4 $166.29   10.847%   $184.3275   $184.33   $184.35   $184.30  
  Purchase #5 $92.66   9.700%   $101.648   $101.65   $101.65   $101.60  
  Purchase #6 $55.88   3.627%   $57.9068   $57.91   $57.90   $57.90  
  Purchase #7 $180.54   9.767%   $198.1733   $198.17   $198.15   $198.20  
  7 purchase totals = $761.73       $833.1359   $833.14   $833.10   $833.10