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	$57.61	11.304%	$64.1222	$64.12	$64.10	$64.10
Purchase #2	$104.49	11.522%	$116.5293	$116.53	$116.55	$116.50
Purchase #3	$162.68	11.416%	$181.2515	$181.25	$181.25	$181.30
Purchase #4	$115.50	6.643%	$123.1727	$123.17	$123.15	$123.20
Purchase #5	$202.79	4.532%	$211.9804	$211.98	$212.00	$212.00
Purchase #6	$49.79	12.119%	$55.8241	$55.82	$55.80	$55.80
Purchase #7	$144.72	4.560%	$151.3192	$151.32	$151.30	$151.30
7 purchase totals =	$837.58		$904.1994	$904.19	$904.15	$904.20