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 $60.83   7.417%   $65.3418   $65.34   $65.35   $65.30  
  Purchase #2 $57.99   12.536%   $65.2596   $65.26   $65.25   $65.30  
  Purchase #3 $83.48   12.629%   $94.0227   $94.02   $94.00   $94.00  
  Purchase #4 $244.96   5.573%   $258.6116   $258.61   $258.60   $258.60  
  Purchase #5 $124.71   11.408%   $138.9369   $138.94   $138.95   $138.90  
  Purchase #6 $38.79   13.321%   $43.9572   $43.96   $43.95   $44.00  
  Purchase #7 $207.29   4.610%   $216.8461   $216.85   $216.85   $216.80  
  7 purchase totals = $818.05       $882.9759   $882.98   $882.95   $882.90