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	$200.89	10.200%	$221.3808	$221.38	$221.40	$221.40
Purchase #2	$219.96	4.554%	$229.977	$229.98	$230.00	$230.00
Purchase #3	$139.82	4.831%	$146.5747	$146.57	$146.55	$146.60
Purchase #4	$197.83	6.802%	$211.2864	$211.29	$211.30	$211.30
Purchase #5	$56.26	7.603%	$60.5374	$60.54	$60.55	$60.50
Purchase #6	$79.89	12.650%	$89.9961	$90.00	$90.00	$90.00
Purchase #7	$216.26	3.140%	$223.0506	$223.05	$223.05	$223.10
7 purchase totals =	$1,110.91		$1,182.8030	$1,182.81	$1,182.85	$1,182.90