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	$86.38	4.322%	$90.1133	$90.11	$90.10	$90.10
Purchase #2	$122.82	11.818%	$137.3349	$137.33	$137.35	$137.30
Purchase #3	$88.48	12.162%	$99.2409	$99.24	$99.25	$99.20
Purchase #4	$195.48	7.102%	$209.363	$209.36	$209.35	$209.40
Purchase #5	$16.61	4.221%	$17.3111	$17.31	$17.30	$17.30
Purchase #6	$17.95	5.508%	$18.9387	$18.94	$18.95	$18.90
Purchase #7	$64.71	7.144%	$69.3329	$69.33	$69.35	$69.30
7 purchase totals =	$592.43		$641.6348	$641.62	$641.65	$641.50