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	$217.87	5.140%	$229.0685	$229.07	$229.05	$229.10
Purchase #2	$78.62	5.358%	$82.8325	$82.83	$82.85	$82.80
Purchase #3	$60.98	6.691%	$65.0602	$65.06	$65.05	$65.10
Purchase #4	$20.35	5.122%	$21.3923	$21.39	$21.40	$21.40
Purchase #5	$15.40	6.397%	$16.3851	$16.39	$16.40	$16.40
Purchase #6	$164.27	12.689%	$185.1142	$185.11	$185.10	$185.10
Purchase #7	$39.92	7.740%	$43.0098	$43.01	$43.00	$43.00
7 purchase totals =	$597.41		$642.8626	$642.86	$642.85	$642.90