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	$170.52	10.610%	$188.6122	$188.61	$188.60	$188.60
Purchase #2	$72.77	3.502%	$75.3184	$75.32	$75.30	$75.30
Purchase #3	$186.67	6.104%	$198.0643	$198.06	$198.05	$198.10
Purchase #4	$12.29	6.611%	$13.1025	$13.10	$13.10	$13.10
Purchase #5	$145.72	3.120%	$150.2665	$150.27	$150.25	$150.30
Purchase #6	$102.90	6.406%	$109.4918	$109.49	$109.50	$109.50
Purchase #7	$144.38	7.483%	$155.184	$155.18	$155.20	$155.20
7 purchase totals =	$835.25		$890.0397	$890.03	$890.00	$890.10