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	$128.58	3.263%	$132.7756	$132.78	$132.80	$132.80
Purchase #2	$155.53	6.700%	$165.9505	$165.95	$165.95	$166.00
Purchase #3	$40.93	6.222%	$43.4767	$43.48	$43.50	$43.50
Purchase #4	$173.91	13.858%	$198.0104	$198.01	$198.00	$198.00
Purchase #5	$38.92	4.755%	$40.7706	$40.77	$40.75	$40.80
Purchase #6	$109.42	9.352%	$119.653	$119.65	$119.65	$119.70
Purchase #7	$93.44	10.477%	$103.2297	$103.23	$103.25	$103.20
7 purchase totals =	$740.73		$803.8665	$803.87	$803.90	$804.00