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	$236.58	10.471%	$261.3523	$261.35	$261.35	$261.40
Purchase #2	$51.74	3.813%	$53.7128	$53.71	$53.70	$53.70
Purchase #3	$214.78	9.147%	$234.4259	$234.43	$234.45	$234.40
Purchase #4	$40.66	8.173%	$43.9831	$43.98	$44.00	$44.00
Purchase #5	$174.25	12.825%	$196.5976	$196.60	$196.60	$196.60
Purchase #6	$141.91	6.235%	$150.7581	$150.76	$150.75	$150.80
Purchase #7	$33.42	6.347%	$35.5412	$35.54	$35.55	$35.50
7 purchase totals =	$893.34		$976.3710	$976.37	$976.40	$976.40