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	$77.90	7.213%	$83.5189	$83.52	$83.50	$83.50
Purchase #2	$96.48	9.354%	$105.5047	$105.50	$105.50	$105.50
Purchase #3	$140.73	3.279%	$145.3445	$145.34	$145.35	$145.30
Purchase #4	$24.78	4.248%	$25.8327	$25.83	$25.85	$25.80
Purchase #5	$215.77	10.287%	$237.9663	$237.97	$237.95	$238.00
Purchase #6	$196.66	13.400%	$223.0124	$223.01	$223.00	$223.00
Purchase #7	$72.27	7.777%	$77.8904	$77.89	$77.90	$77.90
7 purchase totals =	$824.59		$899.0699	$899.06	$899.05	$899.00