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	$37.37	12.588%	$42.0741	$42.07	$42.05	$42.10
Purchase #2	$151.60	6.836%	$161.9634	$161.96	$161.95	$162.00
Purchase #3	$135.36	6.750%	$144.4968	$144.50	$144.50	$144.50
Purchase #4	$217.67	10.288%	$240.0639	$240.06	$240.05	$240.10
Purchase #5	$104.65	6.118%	$111.0525	$111.05	$111.05	$111.10
Purchase #6	$42.46	3.862%	$44.0998	$44.10	$44.10	$44.10
Purchase #7	$159.38	5.427%	$168.0296	$168.03	$168.05	$168.00
7 purchase totals =	$848.49		$911.7801	$911.77	$911.75	$911.90