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	$107.87	12.234%	$121.0668	$121.07	$121.05	$121.10
Purchase #2	$120.93	6.780%	$129.1291	$129.13	$129.15	$129.10
Purchase #3	$137.59	10.513%	$152.0548	$152.05	$152.05	$152.10
Purchase #4	$66.92	8.119%	$72.3532	$72.35	$72.35	$72.40
Purchase #5	$41.88	8.768%	$45.552	$45.55	$45.55	$45.60
Purchase #6	$183.74	6.681%	$196.0157	$196.02	$196.00	$196.00
Purchase #7	$132.78	9.647%	$145.5893	$145.59	$145.60	$145.60
7 purchase totals =	$791.71		$861.7609	$861.76	$861.75	$861.90