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	$36.43	3.117%	$37.5655	$37.57	$37.55	$37.60
Purchase #2	$183.79	6.754%	$196.2032	$196.20	$196.20	$196.20
Purchase #3	$52.28	10.476%	$57.7569	$57.76	$57.75	$57.80
Purchase #4	$210.70	4.694%	$220.5903	$220.59	$220.60	$220.60
Purchase #5	$180.55	5.762%	$190.9533	$190.95	$190.95	$191.00
Purchase #6	$36.25	12.730%	$40.8646	$40.86	$40.85	$40.90
Purchase #7	$206.98	13.285%	$234.4773	$234.48	$234.50	$234.50
7 purchase totals =	$906.98		$978.4111	$978.41	$978.40	$978.60