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	$16.96	11.591%	$18.9258	$18.93	$18.95	$18.90
Purchase #2	$189.26	13.665%	$215.1224	$215.12	$215.10	$215.10
Purchase #3	$62.34	11.637%	$69.5945	$69.59	$69.60	$69.60
Purchase #4	$91.63	8.185%	$99.1299	$99.13	$99.15	$99.10
Purchase #5	$84.91	5.379%	$89.4773	$89.48	$89.50	$89.50
Purchase #6	$29.61	5.740%	$31.3096	$31.31	$31.30	$31.30
Purchase #7	$234.84	7.198%	$251.7438	$251.74	$251.75	$251.70
7 purchase totals =	$709.55		$775.3033	$775.30	$775.35	$775.20