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	$111.63	8.782%	$121.4333	$121.43	$121.45	$121.40
Purchase #2	$64.88	10.149%	$71.4647	$71.46	$71.45	$71.50
Purchase #3	$109.89	12.233%	$123.3328	$123.33	$123.35	$123.30
Purchase #4	$55.59	12.579%	$62.5827	$62.58	$62.60	$62.60
Purchase #5	$163.85	6.209%	$174.0234	$174.02	$174.00	$174.00
Purchase #6	$72.52	7.789%	$78.1686	$78.17	$78.15	$78.20
Purchase #7	$207.25	7.507%	$222.8083	$222.81	$222.80	$222.80
7 purchase totals =	$785.61		$853.8138	$853.80	$853.80	$853.80