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	$26.56	8.181%	$28.7329	$28.73	$28.75	$28.70
Purchase #2	$210.27	6.266%	$223.4455	$223.45	$223.45	$223.40
Purchase #3	$40.71	5.419%	$42.9161	$42.92	$42.90	$42.90
Purchase #4	$61.72	10.560%	$68.2376	$68.24	$68.25	$68.20
Purchase #5	$96.64	3.130%	$99.6648	$99.66	$99.65	$99.70
Purchase #6	$136.55	7.855%	$147.276	$147.28	$147.30	$147.30
Purchase #7	$73.33	13.769%	$83.4268	$83.43	$83.45	$83.40
7 purchase totals =	$645.78		$693.6997	$693.71	$693.75	$693.60