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	$155.98	12.718%	$175.8175	$175.82	$175.80	$175.80
Purchase #2	$81.67	4.514%	$85.3566	$85.36	$85.35	$85.40
Purchase #3	$204.68	3.346%	$211.5286	$211.53	$211.55	$211.50
Purchase #4	$60.77	9.248%	$66.39	$66.39	$66.40	$66.40
Purchase #5	$95.39	8.654%	$103.6451	$103.65	$103.65	$103.60
Purchase #6	$84.96	12.832%	$95.8621	$95.86	$95.85	$95.90
Purchase #7	$48.45	11.823%	$54.1782	$54.18	$54.20	$54.20
7 purchase totals =	$731.90		$792.7781	$792.79	$792.80	$792.80