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 $227.43   11.813%   $254.2963   $254.30   $254.30   $254.30  
  Purchase #2 $107.94   7.371%   $115.8963   $115.90   $115.90   $115.90  
  Purchase #3 $171.59   5.804%   $181.5491   $181.55   $181.55   $181.50  
  Purchase #4 $16.59   6.842%   $17.7251   $17.73   $17.75   $17.70  
  Purchase #5 $175.89   4.585%   $183.9546   $183.95   $183.95   $184.00  
  Purchase #6 $40.99   10.813%   $45.4222   $45.42   $45.40   $45.40  
  Purchase #7 $183.93   11.867%   $205.757   $205.76   $205.75   $205.80  
  7 purchase totals = $924.36       $1,004.6006   $1,004.61   $1,004.60   $1,004.60