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	$16.90	13.517%	$19.1844	$19.18	$19.20	$19.20
Purchase #2	$122.29	9.113%	$133.4343	$133.43	$133.45	$133.40
Purchase #3	$30.63	3.667%	$31.7532	$31.75	$31.75	$31.80
Purchase #4	$204.72	4.479%	$213.8894	$213.89	$213.90	$213.90
Purchase #5	$37.52	12.161%	$42.0828	$42.08	$42.10	$42.10
Purchase #6	$52.69	12.376%	$59.2109	$59.21	$59.20	$59.20
Purchase #7	$196.99	9.544%	$215.7907	$215.79	$215.80	$215.80
7 purchase totals =	$661.74		$715.3457	$715.33	$715.40	$715.40