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	$250.99	9.174%	$274.0158	$274.02	$274.00	$274.00
Purchase #2	$73.80	11.768%	$82.4848	$82.48	$82.50	$82.50
Purchase #3	$165.98	10.565%	$183.5158	$183.52	$183.50	$183.50
Purchase #4	$36.78	3.458%	$38.0519	$38.05	$38.05	$38.10
Purchase #5	$38.42	5.604%	$40.5731	$40.57	$40.55	$40.60
Purchase #6	$53.69	5.321%	$56.5468	$56.55	$56.55	$56.50
Purchase #7	$73.67	6.452%	$78.4232	$78.42	$78.40	$78.40
7 purchase totals =	$693.33		$753.6114	$753.61	$753.55	$753.60