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	$28.33	13.510%	$32.1574	$32.16	$32.15	$32.20
Purchase #2	$235.33	13.772%	$267.7396	$267.74	$267.75	$267.70
Purchase #3	$48.55	10.560%	$53.6769	$53.68	$53.70	$53.70
Purchase #4	$196.89	11.210%	$218.9614	$218.96	$218.95	$219.00
Purchase #5	$249.72	7.528%	$268.5189	$268.52	$268.50	$268.50
Purchase #6	$61.38	13.292%	$69.5386	$69.54	$69.55	$69.50
Purchase #7	$11.40	7.780%	$12.2869	$12.29	$12.30	$12.30
7 purchase totals =	$831.60		$922.8797	$922.89	$922.90	$922.90