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	$37.35	13.128%	$42.2533	$42.25	$42.25	$42.30
Purchase #2	$141.53	11.301%	$157.5243	$157.52	$157.50	$157.50
Purchase #3	$210.78	10.660%	$233.2491	$233.25	$233.25	$233.20
Purchase #4	$50.81	8.485%	$55.1212	$55.12	$55.10	$55.10
Purchase #5	$139.34	13.141%	$157.6507	$157.65	$157.65	$157.70
Purchase #6	$170.54	8.371%	$184.8159	$184.82	$184.80	$184.80
Purchase #7	$194.54	12.545%	$218.945	$218.95	$218.95	$218.90
7 purchase totals =	$944.89		$1,049.5595	$1,049.56	$1,049.50	$1,049.50