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	$153.42	8.331%	$166.2014	$166.20	$166.20	$166.20
Purchase #2	$240.79	10.188%	$265.3217	$265.32	$265.30	$265.30
Purchase #3	$37.84	6.757%	$40.3968	$40.40	$40.40	$40.40
Purchase #4	$87.40	9.547%	$95.7441	$95.74	$95.75	$95.70
Purchase #5	$211.55	9.439%	$231.5182	$231.52	$231.50	$231.50
Purchase #6	$16.72	11.261%	$18.6028	$18.60	$18.60	$18.60
Purchase #7	$248.79	10.119%	$273.9651	$273.97	$273.95	$274.00
7 purchase totals =	$996.51		$1,091.7501	$1,091.75	$1,091.70	$1,091.70