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	$103.99	13.740%	$118.2782	$118.28	$118.30	$118.30
Purchase #2	$106.87	13.123%	$120.8946	$120.89	$120.90	$120.90
Purchase #3	$182.51	3.820%	$189.4819	$189.48	$189.50	$189.50
Purchase #4	$171.26	8.697%	$186.1545	$186.15	$186.15	$186.20
Purchase #5	$119.33	7.822%	$128.664	$128.66	$128.65	$128.70
Purchase #6	$129.35	5.338%	$136.2547	$136.25	$136.25	$136.30
Purchase #7	$87.45	12.827%	$98.6672	$98.67	$98.65	$98.70
7 purchase totals =	$900.76		$978.3951	$978.38	$978.40	$978.60