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	$235.29	9.446%	$257.5155	$257.52	$257.50	$257.50
Purchase #2	$63.81	12.418%	$71.7339	$71.73	$71.75	$71.70
Purchase #3	$210.48	9.612%	$230.7113	$230.71	$230.70	$230.70
Purchase #4	$160.49	5.274%	$168.9542	$168.95	$168.95	$169.00
Purchase #5	$149.96	8.113%	$162.1263	$162.13	$162.15	$162.10
Purchase #6	$40.37	7.629%	$43.4498	$43.45	$43.45	$43.40
Purchase #7	$221.50	10.764%	$245.3423	$245.34	$245.35	$245.30
7 purchase totals =	$1,081.90		$1,179.8333	$1,179.83	$1,179.85	$1,179.70