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	$123.27	3.650%	$127.7694	$127.77	$127.75	$127.80
Purchase #2	$209.98	12.571%	$236.3766	$236.38	$236.40	$236.40
Purchase #3	$199.92	7.852%	$215.6177	$215.62	$215.60	$215.60
Purchase #4	$21.72	4.386%	$22.6726	$22.67	$22.65	$22.70
Purchase #5	$200.76	6.753%	$214.3173	$214.32	$214.30	$214.30
Purchase #6	$153.36	5.654%	$162.031	$162.03	$162.05	$162.00
Purchase #7	$32.77	13.269%	$37.1183	$37.12	$37.10	$37.10
7 purchase totals =	$941.78		$1,015.9029	$1,015.91	$1,015.85	$1,015.90