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	$86.39	9.182%	$94.3223	$94.32	$94.30	$94.30
Purchase #2	$146.74	12.832%	$165.5697	$165.57	$165.55	$165.60
Purchase #3	$40.77	7.370%	$43.7747	$43.77	$43.75	$43.80
Purchase #4	$71.92	10.696%	$79.6126	$79.61	$79.60	$79.60
Purchase #5	$79.70	12.417%	$89.5963	$89.60	$89.60	$89.60
Purchase #6	$136.51	13.499%	$154.9375	$154.94	$154.95	$154.90
Purchase #7	$234.62	10.777%	$259.905	$259.91	$259.90	$259.90
7 purchase totals =	$796.65		$887.7181	$887.72	$887.65	$887.70