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	$90.27	3.592%	$93.5125	$93.51	$93.50	$93.50
Purchase #2	$33.39	4.487%	$34.8882	$34.89	$34.90	$34.90
Purchase #3	$153.99	10.256%	$169.7832	$169.78	$169.80	$169.80
Purchase #4	$104.98	4.647%	$109.8584	$109.86	$109.85	$109.90
Purchase #5	$183.78	11.619%	$205.1334	$205.13	$205.15	$205.10
Purchase #6	$32.55	3.732%	$33.7648	$33.76	$33.75	$33.80
Purchase #7	$90.43	6.234%	$96.0674	$96.07	$96.05	$96.10
7 purchase totals =	$689.39		$743.0079	$743.00	$743.00	$743.10