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 $82.36   13.674%   $93.6219   $93.62   $93.60   $93.60  
  Purchase #2 $209.39   11.157%   $232.7516   $232.75   $232.75   $232.80  
  Purchase #3 $201.47   5.309%   $212.166   $212.17   $212.15   $212.20  
  Purchase #4 $41.70   12.806%   $47.0401   $47.04   $47.05   $47.00  
  Purchase #5 $188.77   5.688%   $199.5072   $199.51   $199.50   $199.50  
  Purchase #6 $46.42   3.348%   $47.9741   $47.97   $47.95   $48.00  
  Purchase #7 $13.51   8.502%   $14.6586   $14.66   $14.65   $14.70  
  7 purchase totals = $783.62       $847.7195   $847.72   $847.65   $847.80