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	$56.70	5.487%	$59.8111	$59.81	$59.80	$59.80
Purchase #2	$152.87	12.106%	$171.3764	$171.38	$171.40	$171.40
Purchase #3	$178.43	9.160%	$194.7742	$194.77	$194.75	$194.80
Purchase #4	$233.99	7.213%	$250.8677	$250.87	$250.85	$250.90
Purchase #5	$244.93	10.418%	$270.4468	$270.45	$270.45	$270.40
Purchase #6	$81.83	10.144%	$90.1308	$90.13	$90.15	$90.10
Purchase #7	$114.67	12.749%	$129.2893	$129.29	$129.30	$129.30
7 purchase totals =	$1,063.42		$1,166.6963	$1,166.70	$1,166.70	$1,166.70