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	$246.72	11.837%	$275.9242	$275.92	$275.90	$275.90
Purchase #2	$76.49	5.316%	$80.5562	$80.56	$80.55	$80.60
Purchase #3	$158.51	6.349%	$168.5738	$168.57	$168.55	$168.60
Purchase #4	$48.47	3.780%	$50.3022	$50.30	$50.30	$50.30
Purchase #5	$101.34	6.731%	$108.1612	$108.16	$108.15	$108.20
Purchase #6	$61.26	9.277%	$66.9431	$66.94	$66.95	$66.90
Purchase #7	$247.69	4.721%	$259.3834	$259.38	$259.40	$259.40
7 purchase totals =	$940.48		$1,009.8441	$1,009.83	$1,009.80	$1,009.90