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	$125.89	12.239%	$141.2977	$141.30	$141.30	$141.30
Purchase #2	$210.61	13.704%	$239.472	$239.47	$239.45	$239.50
Purchase #3	$180.73	3.199%	$186.5116	$186.51	$186.50	$186.50
Purchase #4	$101.43	7.494%	$109.0312	$109.03	$109.05	$109.00
Purchase #5	$216.51	11.562%	$241.5429	$241.54	$241.55	$241.50
Purchase #6	$249.76	11.545%	$278.5948	$278.59	$278.60	$278.60
Purchase #7	$155.27	8.746%	$168.8499	$168.85	$168.85	$168.80
7 purchase totals =	$1,240.20		$1,365.3001	$1,365.29	$1,365.30	$1,365.20