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	$78.79	3.261%	$81.3593	$81.36	$81.35	$81.40
Purchase #2	$117.44	12.479%	$132.0953	$132.10	$132.10	$132.10
Purchase #3	$104.29	13.499%	$118.3681	$118.37	$118.35	$118.40
Purchase #4	$167.28	11.786%	$186.9956	$187.00	$187.00	$187.00
Purchase #5	$49.87	7.713%	$53.7165	$53.72	$53.70	$53.70
Purchase #6	$228.40	11.600%	$254.8944	$254.89	$254.90	$254.90
Purchase #7	$135.83	11.123%	$150.9384	$150.94	$150.95	$150.90
7 purchase totals =	$881.90		$978.3676	$978.38	$978.35	$978.40