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 $48.81   13.773%   $55.5326   $55.53   $55.55   $55.50  
  Purchase #2 $103.88   12.287%   $116.6437   $116.64   $116.65   $116.60  
  Purchase #3 $131.33   3.788%   $136.3048   $136.30   $136.30   $136.30  
  Purchase #4 $217.50   7.765%   $234.3889   $234.39   $234.40   $234.40  
  Purchase #5 $150.33   11.802%   $168.0719   $168.07   $168.05   $168.10  
  Purchase #6 $228.88   7.545%   $246.149   $246.15   $246.15   $246.10  
  Purchase #7 $107.62   6.245%   $114.3409   $114.34   $114.35   $114.30  
  7 purchase totals = $988.35       $1,071.4318   $1,071.42   $1,071.45   $1,071.30