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	$229.26	9.284%	$250.5445	$250.54	$250.55	$250.50
Purchase #2	$55.82	7.458%	$59.9831	$59.98	$60.00	$60.00
Purchase #3	$132.72	7.669%	$142.8983	$142.90	$142.90	$142.90
Purchase #4	$192.86	8.282%	$208.8327	$208.83	$208.85	$208.80
Purchase #5	$89.80	11.261%	$99.9124	$99.91	$99.90	$99.90
Purchase #6	$140.98	7.546%	$151.6184	$151.62	$151.60	$151.60
Purchase #7	$19.31	3.801%	$20.044	$20.04	$20.05	$20.00
7 purchase totals =	$860.75		$933.8334	$933.82	$933.85	$933.70