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	$38.64	8.816%	$42.0465	$42.05	$42.05	$42.00
Purchase #2	$79.96	6.678%	$85.2997	$85.30	$85.30	$85.30
Purchase #3	$39.33	8.275%	$42.5846	$42.58	$42.60	$42.60
Purchase #4	$149.78	10.730%	$165.8514	$165.85	$165.85	$165.90
Purchase #5	$153.75	7.597%	$165.4304	$165.43	$165.45	$165.40
Purchase #6	$218.83	11.298%	$243.5534	$243.55	$243.55	$243.60
Purchase #7	$146.63	11.479%	$163.4617	$163.46	$163.45	$163.50
7 purchase totals =	$826.92		$908.2277	$908.22	$908.25	$908.30