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 $33.62   4.721%   $35.2072   $35.21   $35.20   $35.20  
  Purchase #2 $171.95   9.412%   $188.1339   $188.13   $188.15   $188.10  
  Purchase #3 $239.81   12.232%   $269.1436   $269.14   $269.15   $269.10  
  Purchase #4 $240.73   8.629%   $261.5026   $261.50   $261.50   $261.50  
  Purchase #5 $164.52   3.580%   $170.4098   $170.41   $170.40   $170.40  
  Purchase #6 $165.48   12.607%   $186.3421   $186.34   $186.35   $186.30  
  Purchase #7 $217.87   8.139%   $235.6024   $235.60   $235.60   $235.60  
  7 purchase totals = $1,233.98       $1,346.3416   $1,346.33   $1,346.35   $1,346.20