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	$153.38	5.361%	$161.6027	$161.60	$161.60	$161.60
Purchase #2	$239.70	7.376%	$257.3803	$257.38	$257.40	$257.40
Purchase #3	$60.59	7.720%	$65.2675	$65.27	$65.25	$65.30
Purchase #4	$42.47	3.243%	$43.8473	$43.85	$43.85	$43.80
Purchase #5	$132.62	13.789%	$150.907	$150.91	$150.90	$150.90
Purchase #6	$81.62	7.614%	$87.8345	$87.83	$87.85	$87.80
Purchase #7	$82.49	9.292%	$90.155	$90.16	$90.15	$90.20
7 purchase totals =	$792.87		$856.9943	$857.00	$857.00	$857.00