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	$157.33	7.165%	$168.6027	$168.60	$168.60	$168.60
Purchase #2	$21.83	11.303%	$24.2974	$24.30	$24.30	$24.30
Purchase #3	$181.94	12.136%	$204.0202	$204.02	$204.00	$204.00
Purchase #4	$68.46	13.119%	$77.4413	$77.44	$77.45	$77.40
Purchase #5	$83.33	7.594%	$89.6581	$89.66	$89.65	$89.70
Purchase #6	$38.70	6.781%	$41.3242	$41.32	$41.30	$41.30
Purchase #7	$57.75	4.264%	$60.2125	$60.21	$60.20	$60.20
7 purchase totals =	$609.34		$665.5564	$665.55	$665.50	$665.50