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	$161.67	5.497%	$170.557	$170.56	$170.55	$170.60
Purchase #2	$196.99	6.258%	$209.3176	$209.32	$209.30	$209.30
Purchase #3	$71.84	9.160%	$78.4205	$78.42	$78.40	$78.40
Purchase #4	$56.46	13.241%	$63.9359	$63.94	$63.95	$63.90
Purchase #5	$28.25	12.715%	$31.842	$31.84	$31.85	$31.80
Purchase #6	$248.94	9.773%	$273.2689	$273.27	$273.25	$273.30
Purchase #7	$90.97	8.326%	$98.5442	$98.54	$98.55	$98.50
7 purchase totals =	$855.12		$925.8861	$925.89	$925.85	$925.80