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 $48.61   12.180%   $54.5307   $54.53   $54.55   $54.50  
  Purchase #2 $245.70   11.581%   $274.1545   $274.15   $274.15   $274.20  
  Purchase #3 $86.49   11.125%   $96.112   $96.11   $96.10   $96.10  
  Purchase #4 $189.76   9.814%   $208.383   $208.38   $208.40   $208.40  
  Purchase #5 $107.65   4.574%   $112.5739   $112.57   $112.55   $112.60  
  Purchase #6 $137.92   3.673%   $142.9858   $142.99   $143.00   $143.00  
  Purchase #7 $55.76   12.364%   $62.6542   $62.65   $62.65   $62.70  
  7 purchase totals = $871.89       $951.3941   $951.38   $951.40   $951.50