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	$67.99	10.841%	$75.3608	$75.36	$75.35	$75.40
Purchase #2	$229.70	3.622%	$238.0197	$238.02	$238.00	$238.00
Purchase #3	$140.28	11.369%	$156.2284	$156.23	$156.25	$156.20
Purchase #4	$40.97	3.698%	$42.4851	$42.49	$42.50	$42.50
Purchase #5	$89.33	11.598%	$99.6905	$99.69	$99.70	$99.70
Purchase #6	$180.77	6.533%	$192.5797	$192.58	$192.60	$192.60
Purchase #7	$134.90	5.455%	$142.2588	$142.26	$142.25	$142.30
7 purchase totals =	$883.94		$946.6230	$946.63	$946.65	$946.70