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	$83.85	6.352%	$89.1762	$89.18	$89.20	$89.20
Purchase #2	$250.64	9.107%	$273.4658	$273.47	$273.45	$273.50
Purchase #3	$28.58	3.438%	$29.5626	$29.56	$29.55	$29.60
Purchase #4	$218.37	10.557%	$241.4233	$241.42	$241.40	$241.40
Purchase #5	$140.49	9.115%	$153.2957	$153.30	$153.30	$153.30
Purchase #6	$236.37	7.144%	$253.2563	$253.26	$253.25	$253.30
Purchase #7	$40.63	11.271%	$45.2094	$45.21	$45.20	$45.20
7 purchase totals =	$998.93		$1,085.3893	$1,085.40	$1,085.35	$1,085.50