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 $127.47   4.457%   $133.1513   $133.15   $133.15   $133.20  
  Purchase #2 $226.93   8.377%   $245.9399   $245.94   $245.95   $245.90  
  Purchase #3 $235.35   10.598%   $260.2924   $260.29   $260.30   $260.30  
  Purchase #4 $80.92   13.221%   $91.6184   $91.62   $91.60   $91.60  
  Purchase #5 $126.31   6.413%   $134.4103   $134.41   $134.40   $134.40  
  Purchase #6 $53.35   4.873%   $55.9497   $55.95   $55.95   $55.90  
  Purchase #7 $141.71   8.755%   $154.1167   $154.12   $154.10   $154.10  
  7 purchase totals = $992.04       $1,075.4787   $1,075.48   $1,075.45   $1,075.40