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	$39.52	4.425%	$41.2688	$41.27	$41.25	$41.30
Purchase #2	$72.95	6.662%	$77.8099	$77.81	$77.80	$77.80
Purchase #3	$158.40	10.400%	$174.8736	$174.87	$174.85	$174.90
Purchase #4	$104.38	13.156%	$118.1122	$118.11	$118.10	$118.10
Purchase #5	$245.63	3.770%	$254.8903	$254.89	$254.90	$254.90
Purchase #6	$32.58	3.701%	$33.7858	$33.79	$33.80	$33.80
Purchase #7	$87.33	13.374%	$99.0095	$99.01	$99.00	$99.00
7 purchase totals =	$740.79		$799.7501	$799.75	$799.70	$799.80