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	$6.36	7.427%	$6.8324	$6.83	$6.85	$6.80
Purchase #2	$188.49	5.290%	$198.4611	$198.46	$198.45	$198.50
Purchase #3	$115.87	6.406%	$123.2926	$123.29	$123.30	$123.30
Purchase #4	$131.94	8.663%	$143.37	$143.37	$143.35	$143.40
Purchase #5	$242.80	13.772%	$276.2384	$276.24	$276.25	$276.20
Purchase #6	$73.89	11.369%	$82.2906	$82.29	$82.30	$82.30
Purchase #7	$219.39	10.632%	$242.7155	$242.72	$242.70	$242.70
7 purchase totals =	$978.74		$1,073.2006	$1,073.20	$1,073.20	$1,073.20