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	$239.92	6.747%	$256.1074	$256.11	$256.10	$256.10
Purchase #2	$5.25	6.535%	$5.5931	$5.59	$5.60	$5.60
Purchase #3	$173.79	8.849%	$189.1687	$189.17	$189.15	$189.20
Purchase #4	$196.75	10.837%	$218.0718	$218.07	$218.05	$218.10
Purchase #5	$235.33	7.743%	$253.5516	$253.55	$253.55	$253.60
Purchase #6	$51.73	9.758%	$56.7778	$56.78	$56.80	$56.80
Purchase #7	$39.89	7.516%	$42.8881	$42.89	$42.90	$42.90
7 purchase totals =	$942.66		$1,022.1585	$1,022.16	$1,022.15	$1,022.30