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	$52.72	13.584%	$59.8815	$59.88	$59.90	$59.90
Purchase #2	$128.90	10.768%	$142.78	$142.78	$142.80	$142.80
Purchase #3	$137.91	7.265%	$147.9292	$147.93	$147.95	$147.90
Purchase #4	$152.59	9.355%	$166.8648	$166.86	$166.85	$166.90
Purchase #5	$28.53	5.542%	$30.1111	$30.11	$30.10	$30.10
Purchase #6	$62.34	8.123%	$67.4039	$67.40	$67.40	$67.40
Purchase #7	$126.49	13.833%	$143.9874	$143.99	$144.00	$144.00
7 purchase totals =	$689.48		$758.9579	$758.95	$759.00	$759.00