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 $47.50   4.521%   $49.6475   $49.65   $49.65   $49.60  
  Purchase #2 $61.61   11.449%   $68.6637   $68.66   $68.65   $68.70  
  Purchase #3 $198.61   7.458%   $213.4223   $213.42   $213.40   $213.40  
  Purchase #4 $200.98   7.503%   $216.0595   $216.06   $216.05   $216.10  
  Purchase #5 $216.33   5.253%   $227.6938   $227.69   $227.70   $227.70  
  Purchase #6 $47.75   7.334%   $51.252   $51.25   $51.25   $51.30  
  Purchase #7 $8.34   7.845%   $8.9943   $8.99   $9.00   $9.00  
  7 purchase totals = $781.12       $835.7331   $835.72   $835.70   $835.80