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	$139.38	4.737%	$145.9824	$145.98	$146.00	$146.00
Purchase #2	$191.84	9.747%	$210.5386	$210.54	$210.55	$210.50
Purchase #3	$169.48	11.285%	$188.6058	$188.61	$188.60	$188.60
Purchase #4	$122.74	11.246%	$136.5433	$136.54	$136.55	$136.50
Purchase #5	$54.53	7.197%	$58.4545	$58.45	$58.45	$58.50
Purchase #6	$172.72	13.394%	$195.8541	$195.85	$195.85	$195.90
Purchase #7	$179.35	6.221%	$190.5074	$190.51	$190.50	$190.50
7 purchase totals =	$1,030.04		$1,126.4861	$1,126.48	$1,126.50	$1,126.50