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	$110.52	3.530%	$114.4214	$114.42	$114.40	$114.40
Purchase #2	$84.32	13.688%	$95.8617	$95.86	$95.85	$95.90
Purchase #3	$46.40	6.317%	$49.3311	$49.33	$49.35	$49.30
Purchase #4	$215.66	12.450%	$242.5097	$242.51	$242.50	$242.50
Purchase #5	$110.59	8.446%	$119.9304	$119.93	$119.95	$119.90
Purchase #6	$100.66	7.589%	$108.2991	$108.30	$108.30	$108.30
Purchase #7	$99.74	4.158%	$103.8872	$103.89	$103.90	$103.90
7 purchase totals =	$767.89		$834.2406	$834.24	$834.25	$834.20