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	$69.54	13.231%	$78.7408	$78.74	$78.75	$78.70
Purchase #2	$39.59	10.579%	$43.7782	$43.78	$43.80	$43.80
Purchase #3	$75.54	10.179%	$83.2292	$83.23	$83.25	$83.20
Purchase #4	$139.58	8.506%	$151.4527	$151.45	$151.45	$151.50
Purchase #5	$87.66	5.378%	$92.3744	$92.37	$92.35	$92.40
Purchase #6	$6.88	7.284%	$7.3811	$7.38	$7.40	$7.40
Purchase #7	$64.94	8.582%	$70.5132	$70.51	$70.50	$70.50
7 purchase totals =	$483.73		$527.4696	$527.46	$527.50	$527.50