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	$76.79	7.511%	$82.5577	$82.56	$82.55	$82.60
Purchase #2	$191.72	4.533%	$200.4107	$200.41	$200.40	$200.40
Purchase #3	$46.86	10.459%	$51.7611	$51.76	$51.75	$51.80
Purchase #4	$151.44	10.573%	$167.4518	$167.45	$167.45	$167.50
Purchase #5	$104.77	9.371%	$114.588	$114.59	$114.60	$114.60
Purchase #6	$11.32	9.767%	$12.4256	$12.43	$12.45	$12.40
Purchase #7	$45.70	8.835%	$49.7376	$49.74	$49.75	$49.70
7 purchase totals =	$628.60		$678.9325	$678.94	$678.95	$679.00