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	$82.89	10.179%	$91.3274	$91.33	$91.35	$91.30
Purchase #2	$244.29	12.729%	$275.3857	$275.39	$275.40	$275.40
Purchase #3	$128.45	4.266%	$133.9297	$133.93	$133.95	$133.90
Purchase #4	$81.56	10.160%	$89.8465	$89.85	$89.85	$89.80
Purchase #5	$20.76	8.452%	$22.5146	$22.51	$22.50	$22.50
Purchase #6	$105.63	4.311%	$110.1837	$110.18	$110.20	$110.20
Purchase #7	$134.66	9.428%	$147.3557	$147.36	$147.35	$147.40
7 purchase totals =	$798.24		$870.5433	$870.55	$870.60	$870.50