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	$61.30	7.797%	$66.0796	$66.08	$66.10	$66.10
Purchase #2	$47.40	6.618%	$50.5369	$50.54	$50.55	$50.50
Purchase #3	$44.38	11.529%	$49.4966	$49.50	$49.50	$49.50
Purchase #4	$61.82	9.729%	$67.8345	$67.83	$67.85	$67.80
Purchase #5	$51.79	8.426%	$56.1538	$56.15	$56.15	$56.20
Purchase #6	$18.50	13.134%	$20.9298	$20.93	$20.95	$20.90
Purchase #7	$104.61	8.860%	$113.8784	$113.88	$113.90	$113.90
7 purchase totals =	$389.80		$424.9096	$424.91	$425.00	$424.90