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	$169.67	10.144%	$186.8813	$186.88	$186.90	$186.90
Purchase #2	$120.61	5.332%	$127.0409	$127.04	$127.05	$127.00
Purchase #3	$59.43	6.514%	$63.3013	$63.30	$63.30	$63.30
Purchase #4	$93.79	7.474%	$100.7999	$100.80	$100.80	$100.80
Purchase #5	$85.92	3.750%	$89.142	$89.14	$89.15	$89.10
Purchase #6	$229.60	10.506%	$253.7218	$253.72	$253.70	$253.70
Purchase #7	$230.74	12.322%	$259.1718	$259.17	$259.15	$259.20
7 purchase totals =	$989.76		$1,080.0590	$1,080.05	$1,080.05	$1,080.00