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 $242.95   10.424%   $268.2751   $268.28   $268.30   $268.30  
  Purchase #2 $13.96   4.113%   $14.5342   $14.53   $14.55   $14.50  
  Purchase #3 $58.85   12.779%   $66.3704   $66.37   $66.35   $66.40  
  Purchase #4 $202.60   10.645%   $224.1668   $224.17   $224.15   $224.20  
  Purchase #5 $173.76   13.660%   $197.4956   $197.50   $197.50   $197.50  
  Purchase #6 $22.57   10.665%   $24.9771   $24.98   $25.00   $25.00  
  Purchase #7 $245.32   5.730%   $259.3768   $259.38   $259.40   $259.40  
  7 purchase totals = $960.01       $1,055.1960   $1,055.21   $1,055.25   $1,055.30