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 $71.85   6.297%   $76.3744   $76.37   $76.35   $76.40  
  Purchase #2 $194.40   8.365%   $210.6616   $210.66   $210.65   $210.70  
  Purchase #3 $214.76   3.601%   $222.4935   $222.49   $222.50   $222.50  
  Purchase #4 $88.32   10.132%   $97.2686   $97.27   $97.25   $97.30  
  Purchase #5 $87.76   7.163%   $94.0462   $94.05   $94.05   $94.00  
  Purchase #6 $247.66   13.326%   $280.6632   $280.66   $280.65   $280.70  
  Purchase #7 $147.64   11.711%   $164.9301   $164.93   $164.95   $164.90  
  7 purchase totals = $1,052.39       $1,146.4376   $1,146.43   $1,146.40   $1,146.50