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	$37.90	7.116%	$40.597	$40.60	$40.60	$40.60
Purchase #2	$248.79	7.679%	$267.8946	$267.89	$267.90	$267.90
Purchase #3	$243.56	6.312%	$258.9335	$258.93	$258.95	$258.90
Purchase #4	$115.45	12.706%	$130.1191	$130.12	$130.10	$130.10
Purchase #5	$136.95	13.216%	$155.0493	$155.05	$155.05	$155.00
Purchase #6	$65.71	3.448%	$67.9757	$67.98	$68.00	$68.00
Purchase #7	$129.72	10.648%	$143.5326	$143.53	$143.55	$143.50
7 purchase totals =	$978.08		$1,064.1018	$1,064.10	$1,064.15	$1,064.00