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	$176.46	6.363%	$187.6881	$187.69	$187.70	$187.70
Purchase #2	$159.39	13.736%	$181.2838	$181.28	$181.30	$181.30
Purchase #3	$72.82	8.265%	$78.8386	$78.84	$78.85	$78.80
Purchase #4	$21.37	12.489%	$24.0389	$24.04	$24.05	$24.00
Purchase #5	$145.74	13.160%	$164.9194	$164.92	$164.90	$164.90
Purchase #6	$18.28	12.383%	$20.5436	$20.54	$20.55	$20.50
Purchase #7	$166.28	11.167%	$184.8485	$184.85	$184.85	$184.80
7 purchase totals =	$760.34		$842.1609	$842.16	$842.20	$842.00