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 $157.89   11.237%   $175.6321   $175.63   $175.65   $175.60  
  Purchase #2 $182.83   6.200%   $194.1655   $194.17   $194.15   $194.20  
  Purchase #3 $160.62   3.240%   $165.8241   $165.82   $165.80   $165.80  
  Purchase #4 $210.49   8.358%   $228.0828   $228.08   $228.10   $228.10  
  Purchase #5 $237.39   11.528%   $264.7563   $264.76   $264.75   $264.80  
  Purchase #6 $65.71   3.466%   $67.9875   $67.99   $68.00   $68.00  
  Purchase #7 $154.97   5.680%   $163.7723   $163.77   $163.75   $163.80  
  7 purchase totals = $1,169.90       $1,260.2206   $1,260.22   $1,260.20   $1,260.30