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	$94.78	5.180%	$99.6896	$99.69	$99.70	$99.70
Purchase #2	$238.25	10.450%	$263.1471	$263.15	$263.15	$263.10
Purchase #3	$35.93	6.719%	$38.3441	$38.34	$38.35	$38.30
Purchase #4	$59.92	12.491%	$67.4046	$67.40	$67.40	$67.40
Purchase #5	$90.51	12.334%	$101.6735	$101.67	$101.65	$101.70
Purchase #6	$131.29	7.308%	$140.8847	$140.88	$140.90	$140.90
Purchase #7	$18.36	12.208%	$20.6014	$20.60	$20.60	$20.60
7 purchase totals =	$669.04		$731.7450	$731.73	$731.75	$731.70