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	$79.39	11.738%	$88.7088	$88.71	$88.70	$88.70
Purchase #2	$189.56	3.514%	$196.2211	$196.22	$196.20	$196.20
Purchase #3	$66.34	4.770%	$69.5044	$69.50	$69.50	$69.50
Purchase #4	$102.98	3.696%	$106.7861	$106.79	$106.80	$106.80
Purchase #5	$86.78	3.495%	$89.813	$89.81	$89.80	$89.80
Purchase #6	$29.37	12.476%	$33.0342	$33.03	$33.05	$33.00
Purchase #7	$99.56	6.261%	$105.7935	$105.79	$105.80	$105.80
7 purchase totals =	$653.98		$689.8611	$689.85	$689.85	$689.80