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	$48.76	12.637%	$54.9218	$54.92	$54.90	$54.90
Purchase #2	$51.78	12.264%	$58.1303	$58.13	$58.15	$58.10
Purchase #3	$31.72	3.139%	$32.7157	$32.72	$32.70	$32.70
Purchase #4	$20.54	8.646%	$22.3159	$22.32	$22.30	$22.30
Purchase #5	$25.74	5.362%	$27.1202	$27.12	$27.10	$27.10
Purchase #6	$69.49	4.226%	$72.4266	$72.43	$72.45	$72.40
Purchase #7	$19.75	4.674%	$20.6731	$20.67	$20.65	$20.70
7 purchase totals =	$267.78		$288.3036	$288.31	$288.25	$288.20