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 $216.93   7.360%   $232.896   $232.90   $232.90   $232.90  
  Purchase #2 $118.73   13.596%   $134.8725   $134.87   $134.85   $134.90  
  Purchase #3 $170.87   11.527%   $190.5662   $190.57   $190.55   $190.60  
  Purchase #4 $216.92   4.752%   $227.228   $227.23   $227.25   $227.20  
  Purchase #5 $167.81   7.177%   $179.8537   $179.85   $179.85   $179.90  
  Purchase #6 $62.99   10.486%   $69.5951   $69.60   $69.60   $69.60  
  Purchase #7 $220.84   7.234%   $236.8156   $236.82   $236.80   $236.80  
  7 purchase totals = $1,175.09       $1,271.8271   $1,271.84   $1,271.80   $1,271.90