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	$245.47	4.746%	$257.12	$257.12	$257.10	$257.10
Purchase #2	$178.44	6.210%	$189.5211	$189.52	$189.50	$189.50
Purchase #3	$91.30	9.354%	$99.8402	$99.84	$99.85	$99.80
Purchase #4	$48.82	7.209%	$52.3394	$52.34	$52.35	$52.30
Purchase #5	$179.30	9.610%	$196.5307	$196.53	$196.55	$196.50
Purchase #6	$65.27	8.869%	$71.0588	$71.06	$71.05	$71.10
Purchase #7	$90.80	3.431%	$93.9153	$93.92	$93.90	$93.90
7 purchase totals =	$899.40		$960.3255	$960.33	$960.30	$960.20