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	$73.74	13.381%	$83.6071	$83.61	$83.60	$83.60
Purchase #2	$106.45	4.218%	$110.9401	$110.94	$110.95	$110.90
Purchase #3	$245.89	11.376%	$273.8624	$273.86	$273.85	$273.90
Purchase #4	$31.74	9.723%	$34.8261	$34.83	$34.85	$34.80
Purchase #5	$105.68	7.413%	$113.5141	$113.51	$113.50	$113.50
Purchase #6	$240.29	10.249%	$264.9173	$264.92	$264.90	$264.90
Purchase #7	$246.31	9.637%	$270.0469	$270.05	$270.05	$270.00
7 purchase totals =	$1,050.10		$1,151.7140	$1,151.72	$1,151.70	$1,151.60