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	$113.86	4.406%	$118.8767	$118.88	$118.90	$118.90
Purchase #2	$205.32	11.219%	$228.3549	$228.35	$228.35	$228.40
Purchase #3	$242.96	9.110%	$265.0937	$265.09	$265.10	$265.10
Purchase #4	$55.88	9.867%	$61.3937	$61.39	$61.40	$61.40
Purchase #5	$49.88	9.382%	$54.5597	$54.56	$54.55	$54.60
Purchase #6	$95.43	10.361%	$105.3175	$105.32	$105.30	$105.30
Purchase #7	$133.45	3.340%	$137.9072	$137.91	$137.90	$137.90
7 purchase totals =	$896.78		$971.5034	$971.50	$971.50	$971.60