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	$155.96	6.116%	$165.4985	$165.50	$165.50	$165.50
Purchase #2	$133.61	10.366%	$147.46	$147.46	$147.45	$147.50
Purchase #3	$225.89	11.336%	$251.4969	$251.50	$251.50	$251.50
Purchase #4	$75.99	5.730%	$80.3442	$80.34	$80.35	$80.30
Purchase #5	$157.64	7.507%	$169.474	$169.47	$169.45	$169.50
Purchase #6	$239.59	3.511%	$248.002	$248.00	$248.00	$248.00
Purchase #7	$114.52	13.677%	$130.1829	$130.18	$130.20	$130.20
7 purchase totals =	$1,103.20		$1,192.4585	$1,192.45	$1,192.45	$1,192.50