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 $203.92   11.561%   $227.4952   $227.50   $227.50   $227.50  
  Purchase #2 $130.37   11.762%   $145.7041   $145.70   $145.70   $145.70  
  Purchase #3 $129.39   3.812%   $134.3223   $134.32   $134.30   $134.30  
  Purchase #4 $199.66   13.590%   $226.7938   $226.79   $226.80   $226.80  
  Purchase #5 $211.62   6.397%   $225.1573   $225.16   $225.15   $225.20  
  Purchase #6 $114.62   10.548%   $126.7101   $126.71   $126.70   $126.70  
  Purchase #7 $123.63   5.309%   $130.1935   $130.19   $130.20   $130.20  
  7 purchase totals = $1,113.21       $1,216.3763   $1,216.37   $1,216.35   $1,216.40