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	$115.54	13.553%	$131.1991	$131.20	$131.20	$131.20
Purchase #2	$51.73	8.617%	$56.1876	$56.19	$56.20	$56.20
Purchase #3	$103.97	12.867%	$117.3478	$117.35	$117.35	$117.30
Purchase #4	$89.44	12.565%	$100.6781	$100.68	$100.70	$100.70
Purchase #5	$84.86	5.527%	$89.5502	$89.55	$89.55	$89.60
Purchase #6	$30.98	7.745%	$33.3794	$33.38	$33.40	$33.40
Purchase #7	$233.50	13.340%	$264.6489	$264.65	$264.65	$264.60
7 purchase totals =	$710.02		$792.9911	$793.00	$793.05	$793.00