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	$95.83	12.832%	$108.1269	$108.13	$108.15	$108.10
Purchase #2	$148.78	13.111%	$168.2865	$168.29	$168.30	$168.30
Purchase #3	$213.81	5.475%	$225.5161	$225.52	$225.50	$225.50
Purchase #4	$82.26	11.646%	$91.84	$91.84	$91.85	$91.80
Purchase #5	$27.91	3.612%	$28.9181	$28.92	$28.90	$28.90
Purchase #6	$67.89	5.365%	$71.5323	$71.53	$71.55	$71.50
Purchase #7	$92.29	10.261%	$101.7599	$101.76	$101.75	$101.80
7 purchase totals =	$728.77		$795.9798	$795.99	$796.00	$795.90