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 $167.69   4.628%   $175.4507   $175.45   $175.45   $175.50  
  Purchase #2 $131.97   3.268%   $136.2828   $136.28   $136.30   $136.30  
  Purchase #3 $219.76   9.871%   $241.4525   $241.45   $241.45   $241.50  
  Purchase #4 $87.56   11.776%   $97.8711   $97.87   $97.85   $97.90  
  Purchase #5 $122.45   11.432%   $136.4485   $136.45   $136.45   $136.40  
  Purchase #6 $192.50   7.754%   $207.4265   $207.43   $207.45   $207.40  
  Purchase #7 $231.45   11.528%   $258.1316   $258.13   $258.15   $258.10  
  7 purchase totals = $1,153.38       $1,253.0637   $1,253.06   $1,253.10   $1,253.10