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 $110.78   9.574%   $121.3861   $121.39   $121.40   $121.40  
  Purchase #2 $168.60   7.148%   $180.6515   $180.65   $180.65   $180.70  
  Purchase #3 $83.61   13.856%   $95.195   $95.20   $95.20   $95.20  
  Purchase #4 $28.58   6.840%   $30.5349   $30.53   $30.55   $30.50  
  Purchase #5 $246.54   6.673%   $262.9916   $262.99   $263.00   $263.00  
  Purchase #6 $108.50   3.416%   $112.2064   $112.21   $112.20   $112.20  
  Purchase #7 $61.71   7.412%   $66.2839   $66.28   $66.30   $66.30  
  7 purchase totals = $808.32       $869.2494   $869.25   $869.30   $869.30