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	$176.30	6.224%	$187.2729	$187.27	$187.25	$187.30
Purchase #2	$93.93	13.124%	$106.2574	$106.26	$106.25	$106.30
Purchase #3	$29.62	11.707%	$33.0876	$33.09	$33.10	$33.10
Purchase #4	$137.37	3.584%	$142.2933	$142.29	$142.30	$142.30
Purchase #5	$42.48	7.739%	$45.7675	$45.77	$45.75	$45.80
Purchase #6	$170.47	4.649%	$178.3952	$178.40	$178.40	$178.40
Purchase #7	$121.37	5.258%	$127.7516	$127.75	$127.75	$127.80
7 purchase totals =	$771.54		$820.8255	$820.83	$820.80	$821.00