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	$61.64	4.632%	$64.4952	$64.50	$64.50	$64.50
Purchase #2	$198.75	11.731%	$222.0654	$222.07	$222.05	$222.10
Purchase #3	$150.61	9.619%	$165.0972	$165.10	$165.10	$165.10
Purchase #4	$94.91	10.112%	$104.5073	$104.51	$104.50	$104.50
Purchase #5	$72.42	6.547%	$77.1613	$77.16	$77.15	$77.20
Purchase #6	$113.97	7.409%	$122.414	$122.41	$122.40	$122.40
Purchase #7	$103.49	8.751%	$112.5464	$112.55	$112.55	$112.50
7 purchase totals =	$795.79		$868.2868	$868.30	$868.25	$868.30