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 $118.43   7.345%   $127.1287   $127.13   $127.15   $127.10  
  Purchase #2 $186.37   4.803%   $195.3214   $195.32   $195.30   $195.30  
  Purchase #3 $42.76   10.147%   $47.0989   $47.10   $47.10   $47.10  
  Purchase #4 $125.45   11.314%   $139.6434   $139.64   $139.65   $139.60  
  Purchase #5 $53.70   5.313%   $56.5531   $56.55   $56.55   $56.60  
  Purchase #6 $236.26   9.728%   $259.2434   $259.24   $259.25   $259.20  
  Purchase #7 $170.76   3.190%   $176.2072   $176.21   $176.20   $176.20  
  7 purchase totals = $933.73       $1,001.1961   $1,001.19   $1,001.20   $1,001.10