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	$147.73	3.660%	$153.1369	$153.14	$153.15	$153.10
Purchase #2	$26.64	12.204%	$29.8911	$29.89	$29.90	$29.90
Purchase #3	$131.60	4.799%	$137.9155	$137.92	$137.90	$137.90
Purchase #4	$53.32	11.765%	$59.5931	$59.59	$59.60	$59.60
Purchase #5	$148.79	5.160%	$156.4676	$156.47	$156.45	$156.50
Purchase #6	$135.44	12.138%	$151.8797	$151.88	$151.90	$151.90
Purchase #7	$24.65	8.290%	$26.6935	$26.69	$26.70	$26.70
7 purchase totals =	$668.17		$715.5774	$715.58	$715.60	$715.60