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	$103.73	5.770%	$109.7152	$109.72	$109.70	$109.70
Purchase #2	$40.47	8.365%	$43.8553	$43.86	$43.85	$43.90
Purchase #3	$115.48	11.635%	$128.9161	$128.92	$128.90	$128.90
Purchase #4	$82.52	11.288%	$91.8349	$91.83	$91.85	$91.80
Purchase #5	$44.26	5.789%	$46.8222	$46.82	$46.80	$46.80
Purchase #6	$128.87	4.593%	$134.789	$134.79	$134.80	$134.80
Purchase #7	$79.50	7.294%	$85.2987	$85.30	$85.30	$85.30
7 purchase totals =	$594.83		$641.2314	$641.24	$641.20	$641.20