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	$103.55	5.676%	$109.4275	$109.43	$109.45	$109.40
Purchase #2	$73.67	5.339%	$77.6032	$77.60	$77.60	$77.60
Purchase #3	$181.90	3.633%	$188.5084	$188.51	$188.50	$188.50
Purchase #4	$199.33	7.739%	$214.7561	$214.76	$214.75	$214.80
Purchase #5	$239.41	8.783%	$260.4374	$260.44	$260.45	$260.40
Purchase #6	$210.59	10.645%	$233.0073	$233.01	$233.00	$233.00
Purchase #7	$153.73	12.390%	$172.7771	$172.78	$172.80	$172.80
7 purchase totals =	$1,162.18		$1,256.5170	$1,256.53	$1,256.55	$1,256.50