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	$55.71	8.694%	$60.5534	$60.55	$60.55	$60.60
Purchase #2	$95.42	9.827%	$104.7969	$104.80	$104.80	$104.80
Purchase #3	$173.57	13.362%	$196.7624	$196.76	$196.75	$196.80
Purchase #4	$105.77	6.112%	$112.2347	$112.23	$112.25	$112.20
Purchase #5	$7.42	12.485%	$8.3464	$8.35	$8.35	$8.30
Purchase #6	$244.39	13.855%	$278.2502	$278.25	$278.25	$278.30
Purchase #7	$107.36	3.477%	$111.0929	$111.09	$111.10	$111.10
7 purchase totals =	$789.64		$872.0369	$872.03	$872.05	$872.10