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 $213.66   13.596%   $242.7092   $242.71   $242.70   $242.70  
  Purchase #2 $222.39   6.210%   $236.2004   $236.20   $236.20   $236.20  
  Purchase #3 $160.95   5.490%   $169.7862   $169.79   $169.80   $169.80  
  Purchase #4 $220.71   9.113%   $240.8233   $240.82   $240.80   $240.80  
  Purchase #5 $227.32   12.639%   $256.051   $256.05   $256.05   $256.10  
  Purchase #6 $129.69   7.300%   $139.1574   $139.16   $139.15   $139.20  
  Purchase #7 $73.41   10.609%   $81.1981   $81.20   $81.20   $81.20  
  7 purchase totals = $1,248.13       $1,365.9256   $1,365.93   $1,365.90   $1,366.00