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 $56.41   13.867%   $64.2324   $64.23   $64.25   $64.20  
  Purchase #2 $233.98   12.208%   $262.5443   $262.54   $262.55   $262.50  
  Purchase #3 $193.46   9.179%   $211.2177   $211.22   $211.20   $211.20  
  Purchase #4 $109.69   13.359%   $124.3435   $124.34   $124.35   $124.30  
  Purchase #5 $131.98   12.575%   $148.5765   $148.58   $148.60   $148.60  
  Purchase #6 $170.48   9.310%   $186.3517   $186.35   $186.35   $186.40  
  Purchase #7 $226.76   10.627%   $250.8578   $250.86   $250.85   $250.90  
  7 purchase totals = $1,122.76       $1,248.1239   $1,248.12   $1,248.15   $1,248.10