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	$132.56	12.313%	$148.8821	$148.88	$148.90	$148.90
Purchase #2	$97.63	7.300%	$104.757	$104.76	$104.75	$104.80
Purchase #3	$19.27	6.642%	$20.5499	$20.55	$20.55	$20.50
Purchase #4	$171.35	11.372%	$190.8359	$190.84	$190.85	$190.80
Purchase #5	$9.99	6.666%	$10.6559	$10.66	$10.65	$10.70
Purchase #6	$54.35	13.111%	$61.4758	$61.48	$61.50	$61.50
Purchase #7	$107.59	3.170%	$111.0006	$111.00	$111.00	$111.00
7 purchase totals =	$592.74		$648.1572	$648.17	$648.20	$648.20