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	$69.37	7.429%	$74.5235	$74.52	$74.50	$74.50
Purchase #2	$82.38	9.436%	$90.1534	$90.15	$90.15	$90.20
Purchase #3	$113.36	9.111%	$123.6882	$123.69	$123.70	$123.70
Purchase #4	$67.69	4.781%	$70.9263	$70.93	$70.95	$70.90
Purchase #5	$110.88	6.860%	$118.4864	$118.49	$118.50	$118.50
Purchase #6	$78.69	11.809%	$87.9825	$87.98	$88.00	$88.00
Purchase #7	$248.87	4.430%	$259.8949	$259.89	$259.90	$259.90
7 purchase totals =	$771.24		$825.6552	$825.65	$825.70	$825.70