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	$234.98	8.250%	$254.3659	$254.37	$254.35	$254.40
Purchase #2	$127.41	7.266%	$136.6676	$136.67	$136.65	$136.70
Purchase #3	$15.86	13.788%	$18.0468	$18.05	$18.05	$18.00
Purchase #4	$27.89	12.447%	$31.3615	$31.36	$31.35	$31.40
Purchase #5	$70.60	9.719%	$77.4616	$77.46	$77.45	$77.50
Purchase #6	$164.37	3.127%	$169.5098	$169.51	$169.50	$169.50
Purchase #7	$98.78	3.118%	$101.86	$101.86	$101.85	$101.90
7 purchase totals =	$739.89		$789.2732	$789.28	$789.20	$789.40