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	$20.84	3.177%	$21.5021	$21.50	$21.50	$21.50
Purchase #2	$58.58	3.623%	$60.7024	$60.70	$60.70	$60.70
Purchase #3	$67.41	7.534%	$72.4887	$72.49	$72.50	$72.50
Purchase #4	$182.48	7.458%	$196.0894	$196.09	$196.10	$196.10
Purchase #5	$131.74	7.591%	$141.7404	$141.74	$141.75	$141.70
Purchase #6	$130.51	12.390%	$146.6802	$146.68	$146.70	$146.70
Purchase #7	$63.91	3.282%	$66.0075	$66.01	$66.00	$66.00
7 purchase totals =	$655.47		$705.2107	$705.21	$705.25	$705.20