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	$123.59	6.852%	$132.0584	$132.06	$132.05	$132.10
Purchase #2	$248.90	13.256%	$281.8942	$281.89	$281.90	$281.90
Purchase #3	$144.36	8.144%	$156.1167	$156.12	$156.10	$156.10
Purchase #4	$249.73	11.560%	$278.5988	$278.60	$278.60	$278.60
Purchase #5	$83.90	13.755%	$95.4404	$95.44	$95.45	$95.40
Purchase #6	$70.66	6.427%	$75.2013	$75.20	$75.20	$75.20
Purchase #7	$81.33	12.812%	$91.75	$91.75	$91.75	$91.80
7 purchase totals =	$1,002.47		$1,111.0598	$1,111.06	$1,111.05	$1,111.10