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	$10.51	9.461%	$11.5044	$11.50	$11.50	$11.50
Purchase #2	$160.94	10.805%	$178.3296	$178.33	$178.35	$178.30
Purchase #3	$221.60	9.517%	$242.6897	$242.69	$242.70	$242.70
Purchase #4	$48.82	4.410%	$50.973	$50.97	$50.95	$51.00
Purchase #5	$176.90	4.672%	$185.1648	$185.16	$185.15	$185.20
Purchase #6	$136.37	4.524%	$142.5394	$142.54	$142.55	$142.50
Purchase #7	$76.37	12.556%	$85.959	$85.96	$85.95	$86.00
7 purchase totals =	$831.51		$897.1599	$897.15	$897.15	$897.20