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	$201.74	12.818%	$227.599	$227.60	$227.60	$227.60
Purchase #2	$225.98	3.184%	$233.1752	$233.18	$233.20	$233.20
Purchase #3	$123.45	6.634%	$131.6397	$131.64	$131.65	$131.60
Purchase #4	$153.44	11.655%	$171.3234	$171.32	$171.30	$171.30
Purchase #5	$49.86	12.647%	$56.1658	$56.17	$56.15	$56.20
Purchase #6	$20.71	12.606%	$23.3207	$23.32	$23.30	$23.30
Purchase #7	$215.74	12.802%	$243.359	$243.36	$243.35	$243.40
7 purchase totals =	$990.92		$1,086.5828	$1,086.59	$1,086.55	$1,086.60