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 $233.65   13.219%   $264.5362   $264.54   $264.55   $264.50  
  Purchase #2 $165.80   5.314%   $174.6106   $174.61   $174.60   $174.60  
  Purchase #3 $178.31   6.309%   $189.5596   $189.56   $189.55   $189.60  
  Purchase #4 $238.46   7.717%   $256.862   $256.86   $256.85   $256.90  
  Purchase #5 $15.71   12.150%   $17.6188   $17.62   $17.60   $17.60  
  Purchase #6 $41.45   5.840%   $43.8707   $43.87   $43.85   $43.90  
  Purchase #7 $15.54   4.312%   $16.2101   $16.21   $16.20   $16.20  
  7 purchase totals = $888.92       $963.2680   $963.27   $963.20   $963.30