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	$92.49	7.707%	$99.6182	$99.62	$99.60	$99.60
Purchase #2	$151.61	11.125%	$168.4766	$168.48	$168.50	$168.50
Purchase #3	$126.48	8.684%	$137.4635	$137.46	$137.45	$137.50
Purchase #4	$128.91	7.134%	$138.1064	$138.11	$138.10	$138.10
Purchase #5	$239.56	10.822%	$265.4852	$265.49	$265.50	$265.50
Purchase #6	$55.36	13.119%	$62.6227	$62.62	$62.60	$62.60
Purchase #7	$127.56	5.238%	$134.2416	$134.24	$134.25	$134.20
7 purchase totals =	$921.97		$1,006.0142	$1,006.02	$1,006.00	$1,006.00