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	$11.93	8.788%	$12.9784	$12.98	$13.00	$13.00
Purchase #2	$183.29	7.179%	$196.4484	$196.45	$196.45	$196.40
Purchase #3	$101.99	7.634%	$109.7759	$109.78	$109.80	$109.80
Purchase #4	$123.34	13.452%	$139.9317	$139.93	$139.95	$139.90
Purchase #5	$231.63	3.146%	$238.9171	$238.92	$238.90	$238.90
Purchase #6	$56.96	4.647%	$59.6069	$59.61	$59.60	$59.60
Purchase #7	$165.88	11.711%	$185.3062	$185.31	$185.30	$185.30
7 purchase totals =	$875.02		$942.9646	$942.98	$943.00	$942.90