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 $64.92   13.497%   $73.6823   $73.68   $73.70   $73.70  
  Purchase #2 $65.34   11.574%   $72.9025   $72.90   $72.90   $72.90  
  Purchase #3 $247.76   7.197%   $265.5913   $265.59   $265.60   $265.60  
  Purchase #4 $84.60   3.726%   $87.7522   $87.75   $87.75   $87.80  
  Purchase #5 $98.71   10.536%   $109.1101   $109.11   $109.10   $109.10  
  Purchase #6 $203.61   8.644%   $221.21   $221.21   $221.20   $221.20  
  Purchase #7 $230.41   6.316%   $244.9627   $244.96   $244.95   $245.00  
  7 purchase totals = $995.35       $1,075.2111   $1,075.20   $1,075.20   $1,075.30