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	$109.97	7.624%	$118.3541	$118.35	$118.35	$118.40
Purchase #2	$151.88	13.815%	$172.8622	$172.86	$172.85	$172.90
Purchase #3	$6.46	8.729%	$7.0239	$7.02	$7.00	$7.00
Purchase #4	$201.93	11.611%	$225.3761	$225.38	$225.40	$225.40
Purchase #5	$209.71	7.304%	$225.0272	$225.03	$225.05	$225.00
Purchase #6	$88.33	13.229%	$100.0152	$100.02	$100.00	$100.00
Purchase #7	$71.74	13.510%	$81.4321	$81.43	$81.45	$81.40
7 purchase totals =	$840.02		$930.0908	$930.09	$930.10	$930.10