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 $237.44   8.463%   $257.5345   $257.53   $257.55   $257.50  
  Purchase #2 $65.54   3.117%   $67.5829   $67.58   $67.60   $67.60  
  Purchase #3 $124.96   8.430%   $135.4941   $135.49   $135.50   $135.50  
  Purchase #4 $219.84   13.417%   $249.3359   $249.34   $249.35   $249.30  
  Purchase #5 $158.72   10.382%   $175.1983   $175.20   $175.20   $175.20  
  Purchase #6 $179.96   4.758%   $188.5225   $188.52   $188.50   $188.50  
  Purchase #7 $135.93   13.735%   $154.6   $154.60   $154.60   $154.60  
  7 purchase totals = $1,122.39       $1,228.2682   $1,228.26   $1,228.30   $1,228.20