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	$171.54	12.777%	$193.4577	$193.46	$193.45	$193.50
Purchase #2	$150.62	9.661%	$165.1714	$165.17	$165.15	$165.20
Purchase #3	$200.59	10.743%	$222.1394	$222.14	$222.15	$222.10
Purchase #4	$232.63	11.700%	$259.8477	$259.85	$259.85	$259.80
Purchase #5	$233.92	10.838%	$259.2722	$259.27	$259.25	$259.30
Purchase #6	$169.76	12.554%	$191.0717	$191.07	$191.05	$191.10
Purchase #7	$249.67	10.534%	$275.9702	$275.97	$275.95	$276.00
7 purchase totals =	$1,408.73		$1,566.9303	$1,566.93	$1,566.85	$1,567.00