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	$117.74	12.391%	$132.3292	$132.33	$132.35	$132.30
Purchase #2	$124.95	12.453%	$140.51	$140.51	$140.50	$140.50
Purchase #3	$88.81	10.477%	$98.1146	$98.11	$98.10	$98.10
Purchase #4	$137.81	9.535%	$150.9502	$150.95	$150.95	$151.00
Purchase #5	$20.39	10.831%	$22.5984	$22.60	$22.60	$22.60
Purchase #6	$150.56	9.334%	$164.6133	$164.61	$164.60	$164.60
Purchase #7	$77.36	7.123%	$82.8704	$82.87	$82.85	$82.90
7 purchase totals =	$717.62		$791.9861	$791.98	$791.95	$792.00