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	$80.85	4.358%	$84.3734	$84.37	$84.35	$84.40
Purchase #2	$42.27	3.437%	$43.7228	$43.72	$43.70	$43.70
Purchase #3	$6.85	6.103%	$7.2681	$7.27	$7.25	$7.30
Purchase #4	$14.78	13.787%	$16.8177	$16.82	$16.80	$16.80
Purchase #5	$173.73	13.307%	$196.8483	$196.85	$196.85	$196.80
Purchase #6	$22.49	7.818%	$24.2483	$24.25	$24.25	$24.20
Purchase #7	$190.90	13.676%	$217.0075	$217.01	$217.00	$217.00
7 purchase totals =	$531.87		$590.2861	$590.29	$590.20	$590.20