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 $245.96   12.176%   $275.9081   $275.91   $275.90   $275.90  
  Purchase #2 $118.95   13.272%   $134.737   $134.74   $134.75   $134.70  
  Purchase #3 $56.28   9.716%   $61.7482   $61.75   $61.75   $61.70  
  Purchase #4 $158.57   12.692%   $178.6957   $178.70   $178.70   $178.70  
  Purchase #5 $61.31   8.746%   $66.6722   $66.67   $66.65   $66.70  
  Purchase #6 $8.87   11.555%   $9.8949   $9.89   $9.90   $9.90  
  Purchase #7 $125.87   12.759%   $141.9298   $141.93   $141.95   $141.90  
  7 purchase totals = $775.81       $869.5859   $869.59   $869.60   $869.50