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	$203.97	7.809%	$219.898	$219.90	$219.90	$219.90
Purchase #2	$198.27	12.106%	$222.2726	$222.27	$222.25	$222.30
Purchase #3	$169.40	4.138%	$176.4098	$176.41	$176.40	$176.40
Purchase #4	$105.95	3.654%	$109.8214	$109.82	$109.80	$109.80
Purchase #5	$59.90	5.579%	$63.2418	$63.24	$63.25	$63.20
Purchase #6	$242.84	13.298%	$275.1329	$275.13	$275.15	$275.10
Purchase #7	$68.40	9.253%	$74.7291	$74.73	$74.75	$74.70
7 purchase totals =	$1,048.73		$1,141.5056	$1,141.50	$1,141.50	$1,141.40