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	$6.38	11.262%	$7.0985	$7.10	$7.10	$7.10
Purchase #2	$244.34	4.535%	$255.4208	$255.42	$255.40	$255.40
Purchase #3	$219.99	7.286%	$236.0185	$236.02	$236.00	$236.00
Purchase #4	$124.82	11.869%	$139.6349	$139.63	$139.65	$139.60
Purchase #5	$196.29	13.325%	$222.4456	$222.45	$222.45	$222.40
Purchase #6	$177.89	5.324%	$187.3609	$187.36	$187.35	$187.40
Purchase #7	$96.79	5.630%	$102.2393	$102.24	$102.25	$102.20
7 purchase totals =	$1,066.50		$1,150.2185	$1,150.22	$1,150.20	$1,150.10