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	$93.81	6.496%	$99.9039	$99.90	$99.90	$99.90
Purchase #2	$122.48	4.623%	$128.1423	$128.14	$128.15	$128.10
Purchase #3	$121.32	8.586%	$131.7365	$131.74	$131.75	$131.70
Purchase #4	$148.45	10.462%	$163.9808	$163.98	$164.00	$164.00
Purchase #5	$10.90	3.105%	$11.2384	$11.24	$11.25	$11.20
Purchase #6	$208.37	11.296%	$231.9075	$231.91	$231.90	$231.90
Purchase #7	$64.70	4.210%	$67.4239	$67.42	$67.40	$67.40
7 purchase totals =	$770.03		$834.3333	$834.33	$834.35	$834.20