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	$80.55	5.725%	$85.1615	$85.16	$85.15	$85.20
Purchase #2	$7.91	7.120%	$8.4732	$8.47	$8.45	$8.50
Purchase #3	$83.55	6.408%	$88.9039	$88.90	$88.90	$88.90
Purchase #4	$51.49	6.278%	$54.7225	$54.72	$54.70	$54.70
Purchase #5	$95.81	12.807%	$108.0804	$108.08	$108.10	$108.10
Purchase #6	$70.50	11.406%	$78.5412	$78.54	$78.55	$78.50
Purchase #7	$57.58	12.529%	$64.7942	$64.79	$64.80	$64.80
7 purchase totals =	$447.39		$488.6769	$488.66	$488.65	$488.70