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	$35.91	12.667%	$40.4587	$40.46	$40.45	$40.50
Purchase #2	$7.29	13.135%	$8.2475	$8.25	$8.25	$8.20
Purchase #3	$87.41	10.210%	$96.3346	$96.33	$96.35	$96.30
Purchase #4	$212.68	12.668%	$239.6223	$239.62	$239.60	$239.60
Purchase #5	$77.77	6.646%	$82.9386	$82.94	$82.95	$82.90
Purchase #6	$114.28	11.682%	$127.6302	$127.63	$127.65	$127.60
Purchase #7	$240.36	6.649%	$256.3415	$256.34	$256.35	$256.30
7 purchase totals =	$775.70		$851.5734	$851.57	$851.60	$851.40