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	$126.41	7.162%	$135.4635	$135.46	$135.45	$135.50
Purchase #2	$81.51	4.766%	$85.3948	$85.39	$85.40	$85.40
Purchase #3	$180.29	3.857%	$187.2438	$187.24	$187.25	$187.20
Purchase #4	$121.79	9.104%	$132.8778	$132.88	$132.90	$132.90
Purchase #5	$70.72	11.453%	$78.8196	$78.82	$78.80	$78.80
Purchase #6	$104.54	4.246%	$108.9788	$108.98	$109.00	$109.00
Purchase #7	$82.25	10.355%	$90.767	$90.77	$90.75	$90.80
7 purchase totals =	$767.51		$819.5453	$819.54	$819.55	$819.60