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 $58.68   13.630%   $66.6781   $66.68   $66.70   $66.70  
  Purchase #2 $204.89   4.622%   $214.36   $214.36   $214.35   $214.40  
  Purchase #3 $95.45   12.534%   $107.4137   $107.41   $107.40   $107.40  
  Purchase #4 $166.29   10.396%   $183.5775   $183.58   $183.60   $183.60  
  Purchase #5 $180.99   3.274%   $186.9156   $186.92   $186.90   $186.90  
  Purchase #6 $121.91   11.506%   $135.937   $135.94   $135.95   $135.90  
  Purchase #7 $170.30   5.471%   $179.6171   $179.62   $179.60   $179.60  
  7 purchase totals = $998.51       $1,074.4990   $1,074.51   $1,074.50   $1,074.50