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	$153.59	4.372%	$160.305	$160.31	$160.30	$160.30
Purchase #2	$54.53	13.303%	$61.7841	$61.78	$61.80	$61.80
Purchase #3	$88.79	11.530%	$99.0275	$99.03	$99.05	$99.00
Purchase #4	$180.34	11.281%	$200.6842	$200.68	$200.70	$200.70
Purchase #5	$62.98	12.147%	$70.6302	$70.63	$70.65	$70.60
Purchase #6	$212.99	9.385%	$232.9791	$232.98	$233.00	$233.00
Purchase #7	$70.56	13.545%	$80.1174	$80.12	$80.10	$80.10
7 purchase totals =	$823.78		$905.5275	$905.53	$905.60	$905.50