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	$23.62	4.846%	$24.7646	$24.76	$24.75	$24.80
Purchase #2	$55.78	7.256%	$59.8274	$59.83	$59.85	$59.80
Purchase #3	$145.76	4.286%	$152.0073	$152.01	$152.00	$152.00
Purchase #4	$172.56	4.873%	$180.9688	$180.97	$180.95	$181.00
Purchase #5	$74.57	6.863%	$79.6877	$79.69	$79.70	$79.70
Purchase #6	$77.55	11.573%	$86.5249	$86.52	$86.50	$86.50
Purchase #7	$55.73	10.460%	$61.5594	$61.56	$61.55	$61.60
7 purchase totals =	$605.57		$645.3401	$645.34	$645.30	$645.40