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 $86.49   8.431%   $93.782   $93.78   $93.80   $93.80  
  Purchase #2 $247.86   8.288%   $268.4026   $268.40   $268.40   $268.40  
  Purchase #3 $59.94   11.488%   $66.8259   $66.83   $66.85   $66.80  
  Purchase #4 $161.87   10.867%   $179.4604   $179.46   $179.45   $179.50  
  Purchase #5 $125.68   7.165%   $134.685   $134.69   $134.70   $134.70  
  Purchase #6 $78.51   6.324%   $83.475   $83.48   $83.50   $83.50  
  Purchase #7 $46.70   9.795%   $51.2743   $51.27   $51.25   $51.30  
  7 purchase totals = $807.05       $877.9052   $877.91   $877.95   $878.00