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	$163.41	3.241%	$168.7061	$168.71	$168.70	$168.70
Purchase #2	$200.34	4.378%	$209.1109	$209.11	$209.10	$209.10
Purchase #3	$169.63	9.726%	$186.1282	$186.13	$186.15	$186.10
Purchase #4	$57.61	13.152%	$65.1869	$65.19	$65.20	$65.20
Purchase #5	$200.45	10.593%	$221.6837	$221.68	$221.70	$221.70
Purchase #6	$93.33	11.308%	$103.8838	$103.88	$103.90	$103.90
Purchase #7	$17.73	13.671%	$20.1539	$20.15	$20.15	$20.20
7 purchase totals =	$902.50		$974.8535	$974.85	$974.90	$974.90