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	$42.35	6.713%	$45.193	$45.19	$45.20	$45.20
Purchase #2	$120.84	3.809%	$125.4428	$125.44	$125.45	$125.40
Purchase #3	$65.91	10.287%	$72.6902	$72.69	$72.70	$72.70
Purchase #4	$224.34	8.574%	$243.5749	$243.57	$243.55	$243.60
Purchase #5	$90.50	10.817%	$100.2894	$100.29	$100.30	$100.30
Purchase #6	$83.76	4.830%	$87.8056	$87.81	$87.80	$87.80
Purchase #7	$33.33	7.456%	$35.8151	$35.82	$35.80	$35.80
7 purchase totals =	$661.03		$710.8110	$710.81	$710.80	$710.80