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	$31.30	11.431%	$34.8779	$34.88	$34.90	$34.90
Purchase #2	$61.35	12.831%	$69.2218	$69.22	$69.20	$69.20
Purchase #3	$170.46	11.662%	$190.339	$190.34	$190.35	$190.30
Purchase #4	$52.65	13.196%	$59.5977	$59.60	$59.60	$59.60
Purchase #5	$89.63	10.838%	$99.3441	$99.34	$99.35	$99.30
Purchase #6	$35.31	9.511%	$38.6683	$38.67	$38.65	$38.70
Purchase #7	$124.31	6.648%	$132.5741	$132.57	$132.55	$132.60
7 purchase totals =	$565.01		$624.6229	$624.62	$624.60	$624.60