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	$33.78	10.173%	$37.2164	$37.22	$37.20	$37.20
Purchase #2	$163.62	13.863%	$186.3026	$186.30	$186.30	$186.30
Purchase #3	$216.89	7.595%	$233.3628	$233.36	$233.35	$233.40
Purchase #4	$160.56	3.150%	$165.6176	$165.62	$165.60	$165.60
Purchase #5	$207.58	12.342%	$233.1995	$233.20	$233.20	$233.20
Purchase #6	$89.88	8.438%	$97.4641	$97.46	$97.45	$97.50
Purchase #7	$239.28	12.763%	$269.8193	$269.82	$269.80	$269.80
7 purchase totals =	$1,111.59		$1,222.9823	$1,222.98	$1,222.90	$1,223.00