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	$74.48	11.542%	$83.0765	$83.08	$83.10	$83.10
Purchase #2	$145.92	4.776%	$152.8891	$152.89	$152.90	$152.90
Purchase #3	$143.81	12.738%	$162.1285	$162.13	$162.15	$162.10
Purchase #4	$11.78	13.571%	$13.3787	$13.38	$13.40	$13.40
Purchase #5	$131.47	6.646%	$140.2075	$140.21	$140.20	$140.20
Purchase #6	$116.92	13.224%	$132.3815	$132.38	$132.40	$132.40
Purchase #7	$156.48	3.123%	$161.3669	$161.37	$161.35	$161.40
7 purchase totals =	$780.86		$845.4287	$845.44	$845.50	$845.50