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	$99.80	5.333%	$105.1223	$105.12	$105.10	$105.10
Purchase #2	$50.59	12.667%	$56.9982	$57.00	$57.00	$57.00
Purchase #3	$77.64	3.777%	$80.5725	$80.57	$80.55	$80.60
Purchase #4	$27.45	12.530%	$30.8895	$30.89	$30.90	$30.90
Purchase #5	$87.61	13.873%	$99.7641	$99.76	$99.75	$99.80
Purchase #6	$207.92	3.850%	$215.9249	$215.92	$215.90	$215.90
Purchase #7	$87.57	11.204%	$97.3813	$97.38	$97.40	$97.40
7 purchase totals =	$638.58		$686.6528	$686.64	$686.60	$686.70