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	$101.55	7.580%	$109.2475	$109.25	$109.25	$109.20
Purchase #2	$55.61	4.785%	$58.2709	$58.27	$58.25	$58.30
Purchase #3	$57.82	13.691%	$65.7361	$65.74	$65.75	$65.70
Purchase #4	$83.47	7.200%	$89.4798	$89.48	$89.50	$89.50
Purchase #5	$93.33	11.791%	$104.3345	$104.33	$104.35	$104.30
Purchase #6	$134.38	6.667%	$143.3391	$143.34	$143.35	$143.30
Purchase #7	$110.65	10.695%	$122.484	$122.48	$122.50	$122.50
7 purchase totals =	$636.81		$692.8919	$692.89	$692.95	$692.80