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 $246.29   8.757%   $267.8576   $267.86   $267.85   $267.90  
  Purchase #2 $10.41   5.407%   $10.9729   $10.97   $10.95   $11.00  
  Purchase #3 $188.97   4.637%   $197.7325   $197.73   $197.75   $197.70  
  Purchase #4 $20.70   4.622%   $21.6568   $21.66   $21.65   $21.70  
  Purchase #5 $136.59   6.754%   $145.8153   $145.82   $145.80   $145.80  
  Purchase #6 $59.63   5.489%   $62.9031   $62.90   $62.90   $62.90  
  Purchase #7 $200.38   5.115%   $210.6294   $210.63   $210.65   $210.60  
  7 purchase totals = $862.97       $917.5676   $917.57   $917.55   $917.60