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	$225.89	13.296%	$255.9243	$255.92	$255.90	$255.90
Purchase #2	$38.74	10.208%	$42.6946	$42.69	$42.70	$42.70
Purchase #3	$225.92	10.220%	$249.009	$249.01	$249.00	$249.00
Purchase #4	$96.27	5.729%	$101.7853	$101.79	$101.80	$101.80
Purchase #5	$54.79	7.453%	$58.8735	$58.87	$58.85	$58.90
Purchase #6	$133.89	12.308%	$150.3692	$150.37	$150.35	$150.40
Purchase #7	$236.31	6.562%	$251.8167	$251.82	$251.80	$251.80
7 purchase totals =	$1,011.81		$1,110.4726	$1,110.47	$1,110.40	$1,110.50