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	$112.46	13.421%	$127.5533	$127.55	$127.55	$127.60
Purchase #2	$90.49	9.580%	$99.1589	$99.16	$99.15	$99.20
Purchase #3	$25.35	10.477%	$28.0059	$28.01	$28.00	$28.00
Purchase #4	$34.73	9.612%	$38.0682	$38.07	$38.05	$38.10
Purchase #5	$93.62	4.481%	$97.8151	$97.82	$97.80	$97.80
Purchase #6	$224.70	8.553%	$243.9186	$243.92	$243.90	$243.90
Purchase #7	$215.56	10.435%	$238.0537	$238.05	$238.05	$238.10
7 purchase totals =	$796.91		$872.5737	$872.58	$872.50	$872.70