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	$129.96	5.494%	$137.1	$137.10	$137.10	$137.10
Purchase #2	$104.93	11.401%	$116.8931	$116.89	$116.90	$116.90
Purchase #3	$17.95	3.273%	$18.5375	$18.54	$18.55	$18.50
Purchase #4	$112.27	11.653%	$125.3528	$125.35	$125.35	$125.40
Purchase #5	$81.92	11.249%	$91.1352	$91.14	$91.15	$91.10
Purchase #6	$172.82	4.229%	$180.1286	$180.13	$180.15	$180.10
Purchase #7	$53.43	11.162%	$59.3939	$59.39	$59.40	$59.40
7 purchase totals =	$673.28		$728.5411	$728.54	$728.60	$728.50