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	$36.92	6.814%	$39.4357	$39.44	$39.45	$39.40
Purchase #2	$30.48	4.513%	$31.8556	$31.86	$31.85	$31.90
Purchase #3	$18.90	9.208%	$20.6403	$20.64	$20.65	$20.60
Purchase #4	$167.34	10.824%	$185.4529	$185.45	$185.45	$185.50
Purchase #5	$42.49	7.709%	$45.7656	$45.77	$45.75	$45.80
Purchase #6	$167.55	12.546%	$188.5708	$188.57	$188.55	$188.60
Purchase #7	$71.33	4.709%	$74.6889	$74.69	$74.70	$74.70
7 purchase totals =	$535.01		$586.4098	$586.42	$586.40	$586.50