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	$6.40	7.616%	$6.8874	$6.89	$6.90	$6.90
Purchase #2	$90.77	12.841%	$102.4258	$102.43	$102.45	$102.40
Purchase #3	$162.82	3.503%	$168.5236	$168.52	$168.50	$168.50
Purchase #4	$207.31	10.225%	$228.5074	$228.51	$228.50	$228.50
Purchase #5	$130.83	13.176%	$148.0682	$148.07	$148.05	$148.10
Purchase #6	$178.47	9.760%	$195.8887	$195.89	$195.90	$195.90
Purchase #7	$238.50	4.721%	$249.7596	$249.76	$249.75	$249.80
7 purchase totals =	$1,015.10		$1,100.0607	$1,100.07	$1,100.05	$1,100.10