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	$240.83	11.426%	$268.3472	$268.35	$268.35	$268.30
Purchase #2	$13.86	8.130%	$14.9868	$14.99	$15.00	$15.00
Purchase #3	$234.70	12.708%	$264.5257	$264.53	$264.55	$264.50
Purchase #4	$41.64	3.388%	$43.0508	$43.05	$43.05	$43.10
Purchase #5	$181.30	4.731%	$189.8773	$189.88	$189.90	$189.90
Purchase #6	$83.88	6.333%	$89.1921	$89.19	$89.20	$89.20
Purchase #7	$33.57	12.600%	$37.7998	$37.80	$37.80	$37.80
7 purchase totals =	$829.78		$907.7797	$907.79	$907.85	$907.80