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	$6.35	5.383%	$6.6918	$6.69	$6.70	$6.70
Purchase #2	$37.65	6.687%	$40.1677	$40.17	$40.15	$40.20
Purchase #3	$136.66	13.592%	$155.2348	$155.23	$155.25	$155.20
Purchase #4	$55.59	12.430%	$62.4998	$62.50	$62.50	$62.50
Purchase #5	$194.50	13.769%	$221.2807	$221.28	$221.30	$221.30
Purchase #6	$30.54	7.440%	$32.8122	$32.81	$32.80	$32.80
Purchase #7	$233.60	13.219%	$264.4796	$264.48	$264.50	$264.50
7 purchase totals =	$694.89		$783.1666	$783.16	$783.20	$783.20