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	$163.73	13.169%	$185.2916	$185.29	$185.30	$185.30
Purchase #2	$50.37	10.483%	$55.6503	$55.65	$55.65	$55.70
Purchase #3	$131.47	12.478%	$147.8748	$147.87	$147.85	$147.90
Purchase #4	$136.68	10.318%	$150.7826	$150.78	$150.80	$150.80
Purchase #5	$214.78	11.223%	$238.8848	$238.88	$238.90	$238.90
Purchase #6	$121.54	8.761%	$132.1881	$132.19	$132.20	$132.20
Purchase #7	$234.73	8.735%	$255.2337	$255.23	$255.25	$255.20
7 purchase totals =	$1,053.30		$1,165.9059	$1,165.89	$1,165.95	$1,166.00