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	$89.85	13.392%	$101.8827	$101.88	$101.90	$101.90
Purchase #2	$154.56	13.301%	$175.118	$175.12	$175.10	$175.10
Purchase #3	$63.93	12.390%	$71.8509	$71.85	$71.85	$71.90
Purchase #4	$210.34	7.687%	$226.5088	$226.51	$226.50	$226.50
Purchase #5	$63.77	13.114%	$72.1328	$72.13	$72.15	$72.10
Purchase #6	$250.36	9.240%	$273.4933	$273.49	$273.50	$273.50
Purchase #7	$146.94	13.322%	$166.5153	$166.52	$166.50	$166.50
7 purchase totals =	$979.75		$1,087.5018	$1,087.50	$1,087.50	$1,087.50