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	$28.56	13.103%	$32.3022	$32.30	$32.30	$32.30
Purchase #2	$244.87	9.555%	$268.2673	$268.27	$268.25	$268.30
Purchase #3	$117.91	13.439%	$133.7559	$133.76	$133.75	$133.80
Purchase #4	$218.80	6.250%	$232.475	$232.48	$232.50	$232.50
Purchase #5	$10.94	6.164%	$11.6143	$11.61	$11.60	$11.60
Purchase #6	$247.62	12.761%	$279.2188	$279.22	$279.20	$279.20
Purchase #7	$65.84	10.318%	$72.6334	$72.63	$72.65	$72.60
7 purchase totals =	$934.54		$1,030.2669	$1,030.27	$1,030.25	$1,030.30