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 $6.68   5.573%   $7.0523   $7.05   $7.05   $7.10  
  Purchase #2 $155.88   12.236%   $174.9535   $174.95   $174.95   $175.00  
  Purchase #3 $34.91   13.139%   $39.4968   $39.50   $39.50   $39.50  
  Purchase #4 $105.78   6.753%   $112.9233   $112.92   $112.90   $112.90  
  Purchase #5 $16.78   11.742%   $18.7503   $18.75   $18.75   $18.80  
  Purchase #6 $111.69   5.841%   $118.2138   $118.21   $118.20   $118.20  
  Purchase #7 $22.93   4.217%   $23.897   $23.90   $23.90   $23.90  
  7 purchase totals = $454.65       $495.2870   $495.28   $495.25   $495.40