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	$93.91	9.717%	$103.0352	$103.04	$103.05	$103.00
Purchase #2	$220.36	9.464%	$241.2149	$241.21	$241.20	$241.20
Purchase #3	$38.77	3.748%	$40.2231	$40.22	$40.20	$40.20
Purchase #4	$172.96	13.690%	$196.6382	$196.64	$196.65	$196.60
Purchase #5	$127.37	11.406%	$141.8978	$141.90	$141.90	$141.90
Purchase #6	$216.43	7.730%	$233.16	$233.16	$233.15	$233.20
Purchase #7	$106.37	9.804%	$116.7985	$116.80	$116.80	$116.80
7 purchase totals =	$976.17		$1,072.9677	$1,072.97	$1,072.95	$1,072.90