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	$42.56	6.562%	$45.3528	$45.35	$45.35	$45.40
Purchase #2	$17.55	12.384%	$19.7234	$19.72	$19.70	$19.70
Purchase #3	$29.97	11.502%	$33.4171	$33.42	$33.40	$33.40
Purchase #4	$89.36	10.533%	$98.7723	$98.77	$98.75	$98.80
Purchase #5	$131.81	9.460%	$144.2792	$144.28	$144.30	$144.30
Purchase #6	$186.95	6.598%	$199.285	$199.29	$199.30	$199.30
Purchase #7	$50.90	3.117%	$52.4866	$52.49	$52.50	$52.50
7 purchase totals =	$549.10		$593.3164	$593.32	$593.30	$593.40