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	$23.31	11.157%	$25.9107	$25.91	$25.90	$25.90
Purchase #2	$15.65	9.263%	$17.0997	$17.10	$17.10	$17.10
Purchase #3	$29.89	10.539%	$33.0401	$33.04	$33.05	$33.00
Purchase #4	$38.96	6.336%	$41.4285	$41.43	$41.45	$41.40
Purchase #5	$14.75	6.115%	$15.652	$15.65	$15.65	$15.70
Purchase #6	$71.64	9.499%	$78.4451	$78.45	$78.45	$78.40
Purchase #7	$92.94	7.347%	$99.7683	$99.77	$99.75	$99.80
7 purchase totals =	$287.14		$311.3444	$311.35	$311.35	$311.30