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 $239.89   9.855%   $263.5312   $263.53   $263.55   $263.50  
  Purchase #2 $87.96   8.341%   $95.2967   $95.30   $95.30   $95.30  
  Purchase #3 $104.91   3.799%   $108.8955   $108.90   $108.90   $108.90  
  Purchase #4 $55.67   11.637%   $62.1483   $62.15   $62.15   $62.10  
  Purchase #5 $61.64   11.603%   $68.7921   $68.79   $68.80   $68.80  
  Purchase #6 $128.79   5.744%   $136.1877   $136.19   $136.20   $136.20  
  Purchase #7 $224.62   7.595%   $241.6799   $241.68   $241.70   $241.70  
  7 purchase totals = $903.48       $976.5314   $976.54   $976.60   $976.50