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 $119.86   6.366%   $127.4903   $127.49   $127.50   $127.50  
  Purchase #2 $118.48   4.694%   $124.0415   $124.04   $124.05   $124.00  
  Purchase #3 $131.43   3.430%   $135.938   $135.94   $135.95   $135.90  
  Purchase #4 $76.35   8.772%   $83.0474   $83.05   $83.05   $83.00  
  Purchase #5 $116.36   9.630%   $127.5655   $127.57   $127.55   $127.60  
  Purchase #6 $224.94   9.107%   $245.4253   $245.43   $245.45   $245.40  
  Purchase #7 $161.65   5.104%   $169.9006   $169.90   $169.90   $169.90  
  7 purchase totals = $949.07       $1,013.4086   $1,013.42   $1,013.45   $1,013.30