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	$226.51	13.370%	$256.7944	$256.79	$256.80	$256.80
Purchase #2	$158.52	13.449%	$179.8394	$179.84	$179.85	$179.80
Purchase #3	$115.37	4.510%	$120.5732	$120.57	$120.55	$120.60
Purchase #4	$93.67	5.233%	$98.5718	$98.57	$98.55	$98.60
Purchase #5	$34.59	9.618%	$37.9169	$37.92	$37.90	$37.90
Purchase #6	$52.89	5.389%	$55.7402	$55.74	$55.75	$55.70
Purchase #7	$209.39	6.424%	$222.8412	$222.84	$222.85	$222.80
7 purchase totals =	$890.94		$972.2771	$972.27	$972.25	$972.20