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	$35.25	6.319%	$37.4774	$37.48	$37.50	$37.50
Purchase #2	$54.62	8.823%	$59.4391	$59.44	$59.45	$59.40
Purchase #3	$41.75	6.819%	$44.5969	$44.60	$44.60	$44.60
Purchase #4	$222.78	11.250%	$247.8428	$247.84	$247.85	$247.80
Purchase #5	$124.83	13.229%	$141.3438	$141.34	$141.35	$141.30
Purchase #6	$182.53	3.500%	$188.9186	$188.92	$188.90	$188.90
Purchase #7	$223.42	10.591%	$247.0824	$247.08	$247.10	$247.10
7 purchase totals =	$885.18		$966.7010	$966.70	$966.75	$966.60