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	$84.98	6.473%	$90.4808	$90.48	$90.50	$90.50
Purchase #2	$7.34	10.149%	$8.0849	$8.08	$8.10	$8.10
Purchase #3	$68.47	10.844%	$75.8949	$75.89	$75.90	$75.90
Purchase #4	$99.72	8.476%	$108.1723	$108.17	$108.15	$108.20
Purchase #5	$189.34	12.695%	$213.3767	$213.38	$213.40	$213.40
Purchase #6	$96.64	9.240%	$105.5695	$105.57	$105.55	$105.60
Purchase #7	$45.89	12.701%	$51.7185	$51.72	$51.70	$51.70
7 purchase totals =	$592.38		$653.2976	$653.29	$653.30	$653.40