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	$52.83	12.395%	$59.3783	$59.38	$59.40	$59.40
Purchase #2	$84.49	9.739%	$92.7185	$92.72	$92.70	$92.70
Purchase #3	$209.96	6.644%	$223.9097	$223.91	$223.90	$223.90
Purchase #4	$222.62	12.514%	$250.4787	$250.48	$250.50	$250.50
Purchase #5	$16.49	5.301%	$17.3641	$17.36	$17.35	$17.40
Purchase #6	$96.51	3.705%	$100.0857	$100.09	$100.10	$100.10
Purchase #7	$51.81	5.603%	$54.7129	$54.71	$54.70	$54.70
7 purchase totals =	$734.71		$798.6479	$798.65	$798.65	$798.70