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	$38.84	8.624%	$42.1896	$42.19	$42.20	$42.20
Purchase #2	$235.31	3.802%	$244.2565	$244.26	$244.25	$244.30
Purchase #3	$87.36	13.465%	$99.123	$99.12	$99.10	$99.10
Purchase #4	$23.35	9.103%	$25.4756	$25.48	$25.50	$25.50
Purchase #5	$140.63	4.196%	$146.5308	$146.53	$146.55	$146.50
Purchase #6	$125.38	7.582%	$134.8863	$134.89	$134.90	$134.90
Purchase #7	$30.75	5.143%	$32.3315	$32.33	$32.35	$32.30
7 purchase totals =	$681.62		$724.7933	$724.80	$724.85	$724.80