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	$229.34	12.818%	$258.7368	$258.74	$258.75	$258.70
Purchase #2	$35.94	13.757%	$40.8843	$40.88	$40.90	$40.90
Purchase #3	$172.43	10.570%	$190.6559	$190.66	$190.65	$190.70
Purchase #4	$169.34	9.326%	$185.1326	$185.13	$185.15	$185.10
Purchase #5	$166.26	3.744%	$172.4848	$172.48	$172.50	$172.50
Purchase #6	$51.54	13.435%	$58.4644	$58.46	$58.45	$58.50
Purchase #7	$193.61	13.293%	$219.3466	$219.35	$219.35	$219.30
7 purchase totals =	$1,018.46		$1,125.7054	$1,125.70	$1,125.75	$1,125.70