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	$21.82	3.240%	$22.527	$22.53	$22.55	$22.50
Purchase #2	$142.45	10.729%	$157.7335	$157.73	$157.75	$157.70
Purchase #3	$72.46	7.516%	$77.9061	$77.91	$77.90	$77.90
Purchase #4	$51.89	6.222%	$55.1186	$55.12	$55.10	$55.10
Purchase #5	$190.89	13.358%	$216.3891	$216.39	$216.40	$216.40
Purchase #6	$38.54	13.220%	$43.635	$43.64	$43.65	$43.60
Purchase #7	$18.82	6.553%	$20.0533	$20.05	$20.05	$20.10
7 purchase totals =	$536.87		$593.3626	$593.37	$593.40	$593.30