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	$48.97	8.862%	$53.3097	$53.31	$53.30	$53.30
Purchase #2	$145.49	10.331%	$160.5206	$160.52	$160.50	$160.50
Purchase #3	$250.97	5.277%	$264.2137	$264.21	$264.20	$264.20
Purchase #4	$70.63	3.456%	$73.071	$73.07	$73.05	$73.10
Purchase #5	$152.54	6.815%	$162.9356	$162.94	$162.95	$162.90
Purchase #6	$32.89	12.586%	$37.0295	$37.03	$37.05	$37.00
Purchase #7	$145.46	4.847%	$152.5104	$152.51	$152.50	$152.50
7 purchase totals =	$846.95		$903.5905	$903.59	$903.55	$903.50