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	$66.92	8.175%	$72.3907	$72.39	$72.40	$72.40
Purchase #2	$181.97	3.303%	$187.9805	$187.98	$188.00	$188.00
Purchase #3	$138.48	12.183%	$155.351	$155.35	$155.35	$155.40
Purchase #4	$39.31	7.587%	$42.2924	$42.29	$42.30	$42.30
Purchase #5	$87.38	8.597%	$94.8921	$94.89	$94.90	$94.90
Purchase #6	$103.35	6.742%	$110.3179	$110.32	$110.30	$110.30
Purchase #7	$109.65	7.213%	$117.5591	$117.56	$117.55	$117.60
7 purchase totals =	$727.06		$780.7837	$780.78	$780.80	$780.90