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	$107.50	12.355%	$120.7816	$120.78	$120.80	$120.80
Purchase #2	$111.67	7.265%	$119.7828	$119.78	$119.80	$119.80
Purchase #3	$169.43	6.521%	$180.4785	$180.48	$180.50	$180.50
Purchase #4	$223.35	9.308%	$244.1394	$244.14	$244.15	$244.10
Purchase #5	$102.98	8.546%	$111.7807	$111.78	$111.80	$111.80
Purchase #6	$93.41	13.752%	$106.2557	$106.26	$106.25	$106.30
Purchase #7	$237.95	13.264%	$269.5117	$269.51	$269.50	$269.50
7 purchase totals =	$1,046.29		$1,152.7304	$1,152.73	$1,152.80	$1,152.80