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 $62.78   3.430%   $64.9334   $64.93   $64.95   $64.90  
  Purchase #2 $48.91   10.802%   $54.1933   $54.19   $54.20   $54.20  
  Purchase #3 $67.63   8.822%   $73.5963   $73.60   $73.60   $73.60  
  Purchase #4 $183.35   11.541%   $204.5104   $204.51   $204.50   $204.50  
  Purchase #5 $95.25   4.363%   $99.4058   $99.41   $99.40   $99.40  
  Purchase #6 $52.71   6.644%   $56.2121   $56.21   $56.20   $56.20  
  Purchase #7 $174.93   13.602%   $198.724   $198.72   $198.70   $198.70  
  7 purchase totals = $685.56       $751.5753   $751.57   $751.55   $751.50