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	$95.48	5.564%	$100.7925	$100.79	$100.80	$100.80
Purchase #2	$29.46	4.822%	$30.8806	$30.88	$30.90	$30.90
Purchase #3	$238.41	13.445%	$270.4642	$270.46	$270.45	$270.50
Purchase #4	$165.27	9.102%	$180.3129	$180.31	$180.30	$180.30
Purchase #5	$218.58	6.802%	$233.4478	$233.45	$233.45	$233.40
Purchase #6	$142.89	13.728%	$162.5059	$162.51	$162.50	$162.50
Purchase #7	$66.53	11.286%	$74.0386	$74.04	$74.05	$74.00
7 purchase totals =	$956.62		$1,052.4425	$1,052.44	$1,052.45	$1,052.40