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	$44.29	5.478%	$46.7162	$46.72	$46.70	$46.70
Purchase #2	$33.92	10.194%	$37.3778	$37.38	$37.40	$37.40
Purchase #3	$144.76	7.425%	$155.5084	$155.51	$155.50	$155.50
Purchase #4	$185.73	7.616%	$199.8752	$199.88	$199.90	$199.90
Purchase #5	$17.60	12.865%	$19.8642	$19.86	$19.85	$19.90
Purchase #6	$83.46	6.163%	$88.6036	$88.60	$88.60	$88.60
Purchase #7	$40.29	12.526%	$45.3367	$45.34	$45.35	$45.30
7 purchase totals =	$550.05		$593.2821	$593.29	$593.30	$593.30