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	$83.89	6.383%	$89.2447	$89.24	$89.25	$89.20
Purchase #2	$60.47	5.483%	$63.7856	$63.79	$63.80	$63.80
Purchase #3	$166.97	8.693%	$181.4847	$181.48	$181.50	$181.50
Purchase #4	$100.44	13.616%	$114.1159	$114.12	$114.10	$114.10
Purchase #5	$127.65	13.520%	$144.9083	$144.91	$144.90	$144.90
Purchase #6	$131.98	8.557%	$143.2735	$143.27	$143.25	$143.30
Purchase #7	$141.83	4.316%	$147.9514	$147.95	$147.95	$148.00
7 purchase totals =	$813.23		$884.7641	$884.76	$884.75	$884.80