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 $212.32   8.488%   $230.3417   $230.34   $230.35   $230.30  
  Purchase #2 $115.75   3.424%   $119.7133   $119.71   $119.70   $119.70  
  Purchase #3 $220.29   6.535%   $234.686   $234.69   $234.70   $234.70  
  Purchase #4 $207.89   4.687%   $217.6338   $217.63   $217.65   $217.60  
  Purchase #5 $148.63   7.193%   $159.321   $159.32   $159.30   $159.30  
  Purchase #6 $20.97   9.555%   $22.9737   $22.97   $22.95   $23.00  
  Purchase #7 $196.96   13.456%   $223.4629   $223.46   $223.45   $223.50  
  7 purchase totals = $1,122.81       $1,208.1324   $1,208.12   $1,208.10   $1,208.10