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	$37.53	12.189%	$42.1045	$42.10	$42.10	$42.10
Purchase #2	$68.37	12.331%	$76.8007	$76.80	$76.80	$76.80
Purchase #3	$197.25	9.786%	$216.5529	$216.55	$216.55	$216.60
Purchase #4	$32.30	4.454%	$33.7386	$33.74	$33.75	$33.70
Purchase #5	$29.83	9.342%	$32.6167	$32.62	$32.60	$32.60
Purchase #6	$142.89	7.774%	$153.9983	$154.00	$154.00	$154.00
Purchase #7	$13.26	4.191%	$13.8157	$13.82	$13.80	$13.80
7 purchase totals =	$521.43		$569.6274	$569.63	$569.60	$569.60