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	$91.67	12.647%	$103.2635	$103.26	$103.25	$103.30
Purchase #2	$221.67	9.410%	$242.5291	$242.53	$242.55	$242.50
Purchase #3	$46.80	10.314%	$51.627	$51.63	$51.65	$51.60
Purchase #4	$169.34	8.856%	$184.3368	$184.34	$184.35	$184.30
Purchase #5	$67.93	4.605%	$71.0582	$71.06	$71.05	$71.10
Purchase #6	$9.43	8.327%	$10.2152	$10.22	$10.20	$10.20
Purchase #7	$38.93	4.836%	$40.8127	$40.81	$40.80	$40.80
7 purchase totals =	$645.77		$703.8425	$703.85	$703.85	$703.80