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 $114.59   10.714%   $126.8672   $126.87   $126.85   $126.90  
  Purchase #2 $89.93   9.564%   $98.5309   $98.53   $98.55   $98.50  
  Purchase #3 $104.52   3.543%   $108.2231   $108.22   $108.20   $108.20  
  Purchase #4 $87.75   12.547%   $98.76   $98.76   $98.75   $98.80  
  Purchase #5 $217.86   6.254%   $231.485   $231.49   $231.50   $231.50  
  Purchase #6 $92.82   9.224%   $101.3817   $101.38   $101.40   $101.40  
  Purchase #7 $214.80   8.474%   $233.0022   $233.00   $233.00   $233.00  
  7 purchase totals = $922.27       $998.2501   $998.25   $998.25   $998.30