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	$47.43	6.692%	$50.604	$50.60	$50.60	$50.60
Purchase #2	$56.97	7.109%	$61.02	$61.02	$61.00	$61.00
Purchase #3	$49.69	11.615%	$55.4615	$55.46	$55.45	$55.50
Purchase #4	$67.89	12.267%	$76.2181	$76.22	$76.20	$76.20
Purchase #5	$92.35	8.270%	$99.9873	$99.99	$100.00	$100.00
Purchase #6	$241.39	10.757%	$267.3563	$267.36	$267.35	$267.40
Purchase #7	$196.33	6.795%	$209.6706	$209.67	$209.65	$209.70
7 purchase totals =	$752.05		$820.3178	$820.32	$820.25	$820.40