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 $57.39   12.654%   $64.6521   $64.65   $64.65   $64.70  
  Purchase #2 $249.73   7.464%   $268.3698   $268.37   $268.35   $268.40  
  Purchase #3 $58.45   4.343%   $60.9885   $60.99   $61.00   $61.00  
  Purchase #4 $71.40   10.162%   $78.6557   $78.66   $78.65   $78.70  
  Purchase #5 $61.35   13.529%   $69.65   $69.65   $69.65   $69.70  
  Purchase #6 $198.53   5.746%   $209.9375   $209.94   $209.95   $209.90  
  Purchase #7 $242.43   12.273%   $272.1834   $272.18   $272.20   $272.20  
  7 purchase totals = $939.28       $1,024.4370   $1,024.44   $1,024.45   $1,024.60