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 $211.49   7.784%   $227.9524   $227.95   $227.95   $228.00  
  Purchase #2 $52.51   12.148%   $58.8889   $58.89   $58.90   $58.90  
  Purchase #3 $148.31   7.285%   $159.1144   $159.11   $159.10   $159.10  
  Purchase #4 $242.28   9.461%   $265.2021   $265.20   $265.20   $265.20  
  Purchase #5 $158.76   6.198%   $168.5999   $168.60   $168.60   $168.60  
  Purchase #6 $101.40   11.666%   $113.2293   $113.23   $113.25   $113.20  
  Purchase #7 $129.73   11.157%   $144.204   $144.20   $144.20   $144.20  
  7 purchase totals = $1,044.48       $1,137.1910   $1,137.18   $1,137.20   $1,137.20