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 $243.61   9.606%   $267.0112   $267.01   $267.00   $267.00  
  Purchase #2 $221.32   13.276%   $250.7024   $250.70   $250.70   $250.70  
  Purchase #3 $94.67   7.358%   $101.6358   $101.64   $101.65   $101.60  
  Purchase #4 $202.81   5.285%   $213.5285   $213.53   $213.55   $213.50  
  Purchase #5 $78.90   8.300%   $85.4487   $85.45   $85.45   $85.40  
  Purchase #6 $91.98   13.520%   $104.4157   $104.42   $104.40   $104.40  
  Purchase #7 $241.83   12.810%   $272.8084   $272.81   $272.80   $272.80  
  7 purchase totals = $1,175.12       $1,295.5507   $1,295.56   $1,295.55   $1,295.40