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	$40.48	13.207%	$45.8262	$45.83	$45.85	$45.80
Purchase #2	$129.40	9.549%	$141.7564	$141.76	$141.75	$141.80
Purchase #3	$5.38	9.820%	$5.9083	$5.91	$5.90	$5.90
Purchase #4	$87.48	13.231%	$99.0545	$99.05	$99.05	$99.10
Purchase #5	$128.34	13.683%	$145.9008	$145.90	$145.90	$145.90
Purchase #6	$36.76	11.150%	$40.8587	$40.86	$40.85	$40.90
Purchase #7	$37.51	5.814%	$39.6908	$39.69	$39.70	$39.70
7 purchase totals =	$465.35		$518.9957	$519.00	$519.00	$519.10