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	$73.92	6.427%	$78.6708	$78.67	$78.65	$78.70
Purchase #2	$28.48	13.677%	$32.3752	$32.38	$32.40	$32.40
Purchase #3	$226.90	8.626%	$246.4724	$246.47	$246.45	$246.50
Purchase #4	$40.46	10.299%	$44.627	$44.63	$44.65	$44.60
Purchase #5	$48.90	7.525%	$52.5797	$52.58	$52.60	$52.60
Purchase #6	$94.66	5.556%	$99.9193	$99.92	$99.90	$99.90
Purchase #7	$177.34	4.823%	$185.8931	$185.89	$185.90	$185.90
7 purchase totals =	$690.66		$740.5375	$740.54	$740.55	$740.60