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	$29.80	11.785%	$33.3119	$33.31	$33.30	$33.30
Purchase #2	$127.60	10.352%	$140.8092	$140.81	$140.80	$140.80
Purchase #3	$216.56	12.806%	$244.2927	$244.29	$244.30	$244.30
Purchase #4	$200.41	6.572%	$213.5809	$213.58	$213.60	$213.60
Purchase #5	$89.47	13.208%	$101.2872	$101.29	$101.30	$101.30
Purchase #6	$57.63	10.412%	$63.6304	$63.63	$63.65	$63.60
Purchase #7	$233.89	10.514%	$258.4812	$258.48	$258.50	$258.50
7 purchase totals =	$955.36		$1,055.3935	$1,055.39	$1,055.45	$1,055.40