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	$10.97	12.293%	$12.3185	$12.32	$12.30	$12.30
Purchase #2	$75.56	12.845%	$85.2657	$85.27	$85.25	$85.30
Purchase #3	$243.37	4.843%	$255.1564	$255.16	$255.15	$255.20
Purchase #4	$16.49	11.463%	$18.3802	$18.38	$18.40	$18.40
Purchase #5	$194.48	3.616%	$201.5124	$201.51	$201.50	$201.50
Purchase #6	$213.52	8.585%	$231.8507	$231.85	$231.85	$231.90
Purchase #7	$102.38	7.165%	$109.7155	$109.72	$109.70	$109.70
7 purchase totals =	$856.77		$914.1994	$914.21	$914.15	$914.30