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	$143.33	3.803%	$148.7808	$148.78	$148.80	$148.80
Purchase #2	$235.66	8.370%	$255.3847	$255.38	$255.40	$255.40
Purchase #3	$123.28	9.304%	$134.75	$134.75	$134.75	$134.80
Purchase #4	$14.48	9.676%	$15.8811	$15.88	$15.90	$15.90
Purchase #5	$218.26	10.173%	$240.4636	$240.46	$240.45	$240.50
Purchase #6	$33.57	13.141%	$37.9814	$37.98	$38.00	$38.00
Purchase #7	$232.45	5.251%	$244.6559	$244.66	$244.65	$244.70
7 purchase totals =	$1,001.03		$1,077.8975	$1,077.89	$1,077.95	$1,078.10