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 $107.35   10.617%   $118.7473   $118.75   $118.75   $118.70  
  Purchase #2 $149.95   11.538%   $167.2512   $167.25   $167.25   $167.30  
  Purchase #3 $245.87   8.648%   $267.1328   $267.13   $267.15   $267.10  
  Purchase #4 $157.57   13.760%   $179.2516   $179.25   $179.25   $179.30  
  Purchase #5 $222.66   7.594%   $239.5688   $239.57   $239.55   $239.60  
  Purchase #6 $130.68   10.325%   $144.1727   $144.17   $144.15   $144.20  
  Purchase #7 $236.99   13.301%   $268.512   $268.51   $268.50   $268.50  
  7 purchase totals = $1,251.07       $1,384.6364   $1,384.63   $1,384.60   $1,384.70