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 $241.81   6.167%   $256.7224   $256.72   $256.70   $256.70  
  Purchase #2 $95.36   6.263%   $101.3324   $101.33   $101.35   $101.30  
  Purchase #3 $131.34   4.811%   $137.6588   $137.66   $137.65   $137.70  
  Purchase #4 $42.32   4.120%   $44.0636   $44.06   $44.05   $44.10  
  Purchase #5 $84.71   12.617%   $95.3979   $95.40   $95.40   $95.40  
  Purchase #6 $10.40   4.529%   $10.871   $10.87   $10.85   $10.90  
  Purchase #7 $108.39   8.830%   $117.9608   $117.96   $117.95   $118.00  
  7 purchase totals = $714.33       $764.0069   $764.00   $763.95   $764.10