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	$62.69	4.397%	$65.4465	$65.45	$65.45	$65.40
Purchase #2	$222.86	10.211%	$245.6162	$245.62	$245.60	$245.60
Purchase #3	$37.68	12.355%	$42.3354	$42.34	$42.35	$42.30
Purchase #4	$89.68	12.443%	$100.8389	$100.84	$100.85	$100.80
Purchase #5	$232.70	3.812%	$241.5705	$241.57	$241.55	$241.60
Purchase #6	$128.77	3.380%	$133.1224	$133.12	$133.10	$133.10
Purchase #7	$19.46	6.825%	$20.7881	$20.79	$20.80	$20.80
7 purchase totals =	$793.84		$849.7180	$849.73	$849.70	$849.60