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	$167.61	10.494%	$185.199	$185.20	$185.20	$185.20
Purchase #2	$145.38	13.248%	$164.6399	$164.64	$164.65	$164.60
Purchase #3	$133.31	5.427%	$140.5447	$140.54	$140.55	$140.50
Purchase #4	$100.63	13.374%	$114.0883	$114.09	$114.10	$114.10
Purchase #5	$6.92	8.443%	$7.5043	$7.50	$7.50	$7.50
Purchase #6	$139.64	11.715%	$155.9988	$156.00	$156.00	$156.00
Purchase #7	$93.29	10.418%	$103.009	$103.01	$103.00	$103.00
7 purchase totals =	$786.78		$870.9840	$870.98	$871.00	$870.90