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 $228.46   11.292%   $254.2577   $254.26   $254.25   $254.30  
  Purchase #2 $185.88   11.662%   $207.5573   $207.56   $207.55   $207.60  
  Purchase #3 $48.25   11.519%   $53.8079   $53.81   $53.80   $53.80  
  Purchase #4 $237.85   5.212%   $250.2467   $250.25   $250.25   $250.20  
  Purchase #5 $178.74   8.272%   $193.5254   $193.53   $193.55   $193.50  
  Purchase #6 $98.44   3.804%   $102.1847   $102.18   $102.20   $102.20  
  Purchase #7 $101.64   10.196%   $112.0032   $112.00   $112.00   $112.00  
  7 purchase totals = $1,079.26       $1,173.5829   $1,173.59   $1,173.60   $1,173.60