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	$60.64	12.762%	$68.3789	$68.38	$68.40	$68.40
Purchase #2	$124.96	8.743%	$135.8853	$135.89	$135.90	$135.90
Purchase #3	$89.38	11.300%	$99.4799	$99.48	$99.50	$99.50
Purchase #4	$174.38	7.790%	$187.9642	$187.96	$187.95	$188.00
Purchase #5	$158.94	4.111%	$165.474	$165.47	$165.45	$165.50
Purchase #6	$112.65	9.326%	$123.1557	$123.16	$123.15	$123.20
Purchase #7	$32.48	4.653%	$33.9913	$33.99	$34.00	$34.00
7 purchase totals =	$753.43		$814.3293	$814.33	$814.35	$814.50