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	$16.48	12.393%	$18.5224	$18.52	$18.50	$18.50
Purchase #2	$55.55	13.832%	$63.2337	$63.23	$63.25	$63.20
Purchase #3	$89.36	12.321%	$100.37	$100.37	$100.35	$100.40
Purchase #4	$206.54	7.833%	$222.7183	$222.72	$222.70	$222.70
Purchase #5	$236.79	6.822%	$252.9438	$252.94	$252.95	$252.90
Purchase #6	$109.86	4.346%	$114.6345	$114.63	$114.65	$114.60
Purchase #7	$112.74	13.638%	$128.1155	$128.12	$128.10	$128.10
7 purchase totals =	$827.32		$900.5382	$900.53	$900.50	$900.40