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 $227.25   6.153%   $241.2327   $241.23   $241.25   $241.20  
  Purchase #2 $224.38   12.451%   $252.3176   $252.32   $252.30   $252.30  
  Purchase #3 $178.65   10.795%   $197.9353   $197.94   $197.95   $197.90  
  Purchase #4 $65.71   6.150%   $69.7512   $69.75   $69.75   $69.80  
  Purchase #5 $79.59   6.276%   $84.5851   $84.59   $84.60   $84.60  
  Purchase #6 $97.98   6.431%   $104.2811   $104.28   $104.30   $104.30  
  Purchase #7 $120.46   13.279%   $136.4559   $136.46   $136.45   $136.50  
  7 purchase totals = $994.02       $1,086.5589   $1,086.57   $1,086.60   $1,086.60