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 $43.49   6.535%   $46.3321   $46.33   $46.35   $46.30  
  Purchase #2 $148.99   9.313%   $162.8654   $162.87   $162.85   $162.90  
  Purchase #3 $170.32   12.422%   $191.4772   $191.48   $191.50   $191.50  
  Purchase #4 $56.60   7.102%   $60.6197   $60.62   $60.60   $60.60  
  Purchase #5 $189.88   8.775%   $206.542   $206.54   $206.55   $206.50  
  Purchase #6 $221.74   5.620%   $234.2018   $234.20   $234.20   $234.20  
  Purchase #7 $18.25   13.284%   $20.6743   $20.67   $20.65   $20.70  
  7 purchase totals = $849.27       $922.7125   $922.71   $922.70   $922.70