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 $151.95   13.661%   $172.7079   $172.71   $172.70   $172.70  
  Purchase #2 $173.90   12.242%   $195.1888   $195.19   $195.20   $195.20  
  Purchase #3 $141.54   5.121%   $148.7883   $148.79   $148.80   $148.80  
  Purchase #4 $71.64   7.158%   $76.768   $76.77   $76.75   $76.80  
  Purchase #5 $203.44   6.652%   $216.9728   $216.97   $216.95   $217.00  
  Purchase #6 $50.27   10.684%   $55.6408   $55.64   $55.65   $55.60  
  Purchase #7 $73.43   7.258%   $78.7595   $78.76   $78.75   $78.80  
  7 purchase totals = $866.17       $944.8261   $944.83   $944.80   $944.90