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	$134.73	12.119%	$151.0579	$151.06	$151.05	$151.10
Purchase #2	$155.41	12.554%	$174.9202	$174.92	$174.90	$174.90
Purchase #3	$211.63	10.127%	$233.0618	$233.06	$233.05	$233.10
Purchase #4	$140.32	13.390%	$159.1088	$159.11	$159.10	$159.10
Purchase #5	$79.52	8.140%	$85.9929	$85.99	$86.00	$86.00
Purchase #6	$132.50	12.369%	$148.8889	$148.89	$148.90	$148.90
Purchase #7	$26.43	8.830%	$28.7638	$28.76	$28.75	$28.80
7 purchase totals =	$880.54		$981.7943	$981.79	$981.75	$981.90