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	$116.82	6.329%	$124.2135	$124.21	$124.20	$124.20
Purchase #2	$163.36	3.111%	$168.4421	$168.44	$168.45	$168.40
Purchase #3	$34.63	13.501%	$39.3054	$39.31	$39.30	$39.30
Purchase #4	$236.71	7.776%	$255.1166	$255.12	$255.10	$255.10
Purchase #5	$128.74	12.821%	$145.2458	$145.25	$145.25	$145.20
Purchase #6	$15.37	11.158%	$17.085	$17.09	$17.10	$17.10
Purchase #7	$139.89	7.749%	$150.7301	$150.73	$150.75	$150.70
7 purchase totals =	$835.52		$900.1385	$900.15	$900.15	$900.00