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	$215.84	6.475%	$229.8156	$229.82	$229.80	$229.80
Purchase #2	$94.97	4.370%	$99.1202	$99.12	$99.10	$99.10
Purchase #3	$190.40	11.127%	$211.5858	$211.59	$211.60	$211.60
Purchase #4	$215.65	9.391%	$235.9017	$235.90	$235.90	$235.90
Purchase #5	$31.58	3.643%	$32.7305	$32.73	$32.75	$32.70
Purchase #6	$137.90	13.789%	$156.915	$156.92	$156.90	$156.90
Purchase #7	$34.87	5.576%	$36.8144	$36.81	$36.80	$36.80
7 purchase totals =	$921.21		$1,002.8832	$1,002.89	$1,002.85	$1,002.80