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	$137.35	9.369%	$150.2183	$150.22	$150.20	$150.20
Purchase #2	$129.61	9.344%	$141.7208	$141.72	$141.70	$141.70
Purchase #3	$134.43	3.456%	$139.0759	$139.08	$139.10	$139.10
Purchase #4	$78.41	10.738%	$86.8297	$86.83	$86.85	$86.80
Purchase #5	$134.75	13.814%	$153.3644	$153.36	$153.35	$153.40
Purchase #6	$207.29	11.504%	$231.1366	$231.14	$231.15	$231.10
Purchase #7	$171.25	11.411%	$190.7913	$190.79	$190.80	$190.80
7 purchase totals =	$993.09		$1,093.1370	$1,093.14	$1,093.15	$1,093.10