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	$47.75	13.724%	$54.3032	$54.30	$54.30	$54.30
Purchase #2	$54.62	11.251%	$60.7653	$60.77	$60.75	$60.80
Purchase #3	$85.38	3.529%	$88.3931	$88.39	$88.40	$88.40
Purchase #4	$34.28	12.786%	$38.663	$38.66	$38.65	$38.70
Purchase #5	$13.53	13.814%	$15.399	$15.40	$15.40	$15.40
Purchase #6	$152.36	13.821%	$173.4177	$173.42	$173.40	$173.40
Purchase #7	$70.34	12.148%	$78.8849	$78.88	$78.90	$78.90
7 purchase totals =	$458.26		$509.8262	$509.82	$509.80	$509.90