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	$89.40	4.110%	$93.0743	$93.07	$93.05	$93.10
Purchase #2	$64.96	11.629%	$72.5142	$72.51	$72.50	$72.50
Purchase #3	$212.62	7.474%	$228.5112	$228.51	$228.50	$228.50
Purchase #4	$41.88	8.709%	$45.5273	$45.53	$45.55	$45.50
Purchase #5	$77.68	3.806%	$80.6365	$80.64	$80.65	$80.60
Purchase #6	$133.53	5.530%	$140.9142	$140.91	$140.90	$140.90
Purchase #7	$45.83	9.715%	$50.2824	$50.28	$50.30	$50.30
7 purchase totals =	$665.90		$711.4601	$711.45	$711.45	$711.40