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 $58.51   8.763%   $63.6372   $63.64   $63.65   $63.60  
  Purchase #2 $15.32   12.202%   $17.1893   $17.19   $17.20   $17.20  
  Purchase #3 $118.51   11.164%   $131.7405   $131.74   $131.75   $131.70  
  Purchase #4 $96.96   3.369%   $100.2266   $100.23   $100.25   $100.20  
  Purchase #5 $57.25   10.811%   $63.4393   $63.44   $63.45   $63.40  
  Purchase #6 $142.63   6.782%   $152.3032   $152.30   $152.30   $152.30  
  Purchase #7 $204.56   12.486%   $230.1014   $230.10   $230.10   $230.10  
  7 purchase totals = $693.74       $758.6375   $758.64   $758.70   $758.50