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 $75.49   7.220%   $80.9404   $80.94   $80.95   $80.90  
  Purchase #2 $178.42   5.278%   $187.837   $187.84   $187.85   $187.80  
  Purchase #3 $32.40   5.473%   $34.1733   $34.17   $34.15   $34.20  
  Purchase #4 $244.94   4.775%   $256.6359   $256.64   $256.65   $256.60  
  Purchase #5 $38.35   6.124%   $40.6986   $40.70   $40.70   $40.70  
  Purchase #6 $92.48   11.543%   $103.155   $103.16   $103.15   $103.20  
  Purchase #7 $32.79   11.260%   $36.4822   $36.48   $36.50   $36.50  
  7 purchase totals = $694.87       $739.9224   $739.93   $739.95   $739.90