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	$27.31	4.319%	$28.4895	$28.49	$28.50	$28.50
Purchase #2	$15.79	8.624%	$17.1517	$17.15	$17.15	$17.20
Purchase #3	$203.90	10.650%	$225.6154	$225.62	$225.60	$225.60
Purchase #4	$168.74	9.395%	$184.5931	$184.59	$184.60	$184.60
Purchase #5	$212.59	10.801%	$235.5518	$235.55	$235.55	$235.60
Purchase #6	$194.86	11.163%	$216.6122	$216.61	$216.60	$216.60
Purchase #7	$210.58	6.258%	$223.7581	$223.76	$223.75	$223.80
7 purchase totals =	$1,033.77		$1,131.7718	$1,131.77	$1,131.75	$1,131.90