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 $55.68   4.199%   $58.018   $58.02   $58.00   $58.00  
  Purchase #2 $58.33   4.467%   $60.9356   $60.94   $60.95   $60.90  
  Purchase #3 $18.59   3.243%   $19.1929   $19.19   $19.20   $19.20  
  Purchase #4 $235.82   11.308%   $262.4865   $262.49   $262.50   $262.50  
  Purchase #5 $94.45   10.485%   $104.3531   $104.35   $104.35   $104.40  
  Purchase #6 $199.98   6.624%   $213.2267   $213.23   $213.25   $213.20  
  Purchase #7 $72.96   5.592%   $77.0399   $77.04   $77.05   $77.00  
  7 purchase totals = $735.81       $795.2527   $795.26   $795.30   $795.20