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 $51.95   11.346%   $57.8442   $57.84   $57.85   $57.80  
  Purchase #2 $173.86   11.798%   $194.372   $194.37   $194.35   $194.40  
  Purchase #3 $76.61   10.802%   $84.8854   $84.89   $84.90   $84.90  
  Purchase #4 $184.73   3.168%   $190.5822   $190.58   $190.60   $190.60  
  Purchase #5 $90.55   5.772%   $95.7765   $95.78   $95.80   $95.80  
  Purchase #6 $91.97   11.432%   $102.484   $102.48   $102.50   $102.50  
  Purchase #7 $218.78   12.801%   $246.786   $246.79   $246.80   $246.80  
  7 purchase totals = $888.45       $972.7303   $972.73   $972.80   $972.80