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	$151.25	13.690%	$171.9561	$171.96	$171.95	$172.00
Purchase #2	$99.91	11.808%	$111.7074	$111.71	$111.70	$111.70
Purchase #3	$24.96	13.757%	$28.3937	$28.39	$28.40	$28.40
Purchase #4	$148.32	5.642%	$156.6882	$156.69	$156.70	$156.70
Purchase #5	$25.74	8.410%	$27.9047	$27.90	$27.90	$27.90
Purchase #6	$100.79	5.376%	$106.2085	$106.21	$106.20	$106.20
Purchase #7	$59.87	9.374%	$65.4822	$65.48	$65.50	$65.50
7 purchase totals =	$610.84		$668.3408	$668.34	$668.35	$668.40