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 $43.74   11.238%   $48.6555   $48.66   $48.65   $48.70  
  Purchase #2 $104.99   5.464%   $110.7267   $110.73   $110.75   $110.70  
  Purchase #3 $99.93   11.483%   $111.405   $111.41   $111.40   $111.40  
  Purchase #4 $125.88   5.336%   $132.597   $132.60   $132.60   $132.60  
  Purchase #5 $195.86   7.213%   $209.9874   $209.99   $210.00   $210.00  
  Purchase #6 $157.50   5.310%   $165.8633   $165.86   $165.85   $165.90  
  Purchase #7 $66.48   12.495%   $74.7867   $74.79   $74.80   $74.80  
  7 purchase totals = $794.38       $854.0216   $854.04   $854.05   $854.10