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	$191.85	12.780%	$216.3684	$216.37	$216.35	$216.40
Purchase #2	$66.36	8.454%	$71.9701	$71.97	$71.95	$72.00
Purchase #3	$96.83	13.490%	$109.8924	$109.89	$109.90	$109.90
Purchase #4	$97.60	3.551%	$101.0658	$101.07	$101.05	$101.10
Purchase #5	$49.75	11.669%	$55.5553	$55.56	$55.55	$55.60
Purchase #6	$72.78	8.813%	$79.1941	$79.19	$79.20	$79.20
Purchase #7	$29.60	6.859%	$31.6303	$31.63	$31.65	$31.60
7 purchase totals =	$604.77		$665.6764	$665.68	$665.65	$665.80