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 $91.55   4.844%   $95.9847   $95.98   $96.00   $96.00  
  Purchase #2 $56.80   6.646%   $60.5749   $60.57   $60.55   $60.60  
  Purchase #3 $187.92   4.543%   $196.4572   $196.46   $196.45   $196.50  
  Purchase #4 $130.99   8.660%   $142.3337   $142.33   $142.35   $142.30  
  Purchase #5 $189.78   8.566%   $206.0366   $206.04   $206.05   $206.00  
  Purchase #6 $196.79   3.540%   $203.7564   $203.76   $203.75   $203.80  
  Purchase #7 $6.88   4.249%   $7.1723   $7.17   $7.15   $7.20  
  7 purchase totals = $860.71       $912.3158   $912.31   $912.30   $912.40