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	$60.77	6.508%	$64.7249	$64.72	$64.70	$64.70
Purchase #2	$148.93	13.296%	$168.7317	$168.73	$168.75	$168.70
Purchase #3	$233.25	13.342%	$264.3702	$264.37	$264.35	$264.40
Purchase #4	$158.87	8.408%	$172.2278	$172.23	$172.25	$172.20
Purchase #5	$242.91	9.204%	$265.2674	$265.27	$265.25	$265.30
Purchase #6	$240.48	9.527%	$263.3905	$263.39	$263.40	$263.40
Purchase #7	$27.29	9.518%	$29.8875	$29.89	$29.90	$29.90
7 purchase totals =	$1,112.50		$1,228.6000	$1,228.60	$1,228.60	$1,228.60