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	$225.35	13.263%	$255.2382	$255.24	$255.25	$255.20
Purchase #2	$52.85	8.312%	$57.2429	$57.24	$57.25	$57.20
Purchase #3	$194.70	13.861%	$221.6874	$221.69	$221.70	$221.70
Purchase #4	$50.85	5.323%	$53.5567	$53.56	$53.55	$53.60
Purchase #5	$48.96	4.456%	$51.1417	$51.14	$51.15	$51.10
Purchase #6	$25.89	6.264%	$27.5117	$27.51	$27.50	$27.50
Purchase #7	$6.93	8.472%	$7.5171	$7.52	$7.50	$7.50
7 purchase totals =	$605.53		$673.8957	$673.90	$673.90	$673.80