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	$111.46	7.221%	$119.5085	$119.51	$119.50	$119.50
Purchase #2	$133.33	12.333%	$149.7736	$149.77	$149.75	$149.80
Purchase #3	$90.75	13.251%	$102.7753	$102.78	$102.80	$102.80
Purchase #4	$16.59	10.622%	$18.3522	$18.35	$18.35	$18.40
Purchase #5	$118.96	10.466%	$131.4104	$131.41	$131.40	$131.40
Purchase #6	$36.49	10.272%	$40.2383	$40.24	$40.25	$40.20
Purchase #7	$117.99	11.538%	$131.6037	$131.60	$131.60	$131.60
7 purchase totals =	$625.57		$693.6620	$693.66	$693.65	$693.70