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	$90.66	9.475%	$99.25	$99.25	$99.25	$99.30
Purchase #2	$234.78	12.424%	$263.9491	$263.95	$263.95	$263.90
Purchase #3	$232.80	11.800%	$260.2704	$260.27	$260.25	$260.30
Purchase #4	$47.75	5.659%	$50.4522	$50.45	$50.45	$50.50
Purchase #5	$208.64	7.797%	$224.9077	$224.91	$224.90	$224.90
Purchase #6	$84.83	3.482%	$87.7838	$87.78	$87.80	$87.80
Purchase #7	$182.89	7.623%	$196.8317	$196.83	$196.85	$196.80
7 purchase totals =	$1,082.35		$1,183.4449	$1,183.44	$1,183.45	$1,183.50