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	$97.96	5.466%	$103.3145	$103.31	$103.30	$103.30
Purchase #2	$168.80	10.132%	$185.9028	$185.90	$185.90	$185.90
Purchase #3	$148.63	6.305%	$158.0011	$158.00	$158.00	$158.00
Purchase #4	$14.90	11.364%	$16.5932	$16.59	$16.60	$16.60
Purchase #5	$88.57	11.184%	$98.4757	$98.48	$98.50	$98.50
Purchase #6	$50.43	6.779%	$53.8486	$53.85	$53.85	$53.80
Purchase #7	$109.98	13.239%	$124.5403	$124.54	$124.55	$124.50
7 purchase totals =	$679.27		$740.6762	$740.67	$740.70	$740.60