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	$235.89	12.349%	$265.0201	$265.02	$265.00	$265.00
Purchase #2	$89.47	11.117%	$99.4164	$99.42	$99.40	$99.40
Purchase #3	$229.27	10.143%	$252.5249	$252.52	$252.50	$252.50
Purchase #4	$30.58	5.389%	$32.228	$32.23	$32.25	$32.20
Purchase #5	$59.49	4.500%	$62.1671	$62.17	$62.15	$62.20
Purchase #6	$245.93	7.605%	$264.633	$264.63	$264.65	$264.60
Purchase #7	$95.74	6.473%	$101.9373	$101.94	$101.95	$101.90
7 purchase totals =	$986.37		$1,077.9268	$1,077.93	$1,077.90	$1,077.80