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 $203.53   10.359%   $224.6137   $224.61   $224.60   $224.60  
  Purchase #2 $50.84   7.181%   $54.4908   $54.49   $54.50   $54.50  
  Purchase #3 $159.77   6.648%   $170.3915   $170.39   $170.40   $170.40  
  Purchase #4 $248.56   11.182%   $276.354   $276.35   $276.35   $276.40  
  Purchase #5 $220.31   5.765%   $233.0109   $233.01   $233.00   $233.00  
  Purchase #6 $182.99   7.864%   $197.3803   $197.38   $197.40   $197.40  
  Purchase #7 $46.37   3.623%   $48.05   $48.05   $48.05   $48.10  
  7 purchase totals = $1,112.37       $1,204.2912   $1,204.28   $1,204.30   $1,204.40