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	$170.87	12.770%	$192.6901	$192.69	$192.70	$192.70
Purchase #2	$95.37	10.637%	$105.5145	$105.51	$105.50	$105.50
Purchase #3	$202.88	10.214%	$223.6022	$223.60	$223.60	$223.60
Purchase #4	$179.88	13.282%	$203.7717	$203.77	$203.75	$203.80
Purchase #5	$128.27	12.225%	$143.951	$143.95	$143.95	$144.00
Purchase #6	$61.26	4.106%	$63.7753	$63.78	$63.80	$63.80
Purchase #7	$41.72	3.313%	$43.1022	$43.10	$43.10	$43.10
7 purchase totals =	$880.25		$976.4070	$976.40	$976.40	$976.50