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	$33.64	5.366%	$35.4451	$35.45	$35.45	$35.40
Purchase #2	$192.76	11.766%	$215.4401	$215.44	$215.45	$215.40
Purchase #3	$152.67	8.383%	$165.4683	$165.47	$165.45	$165.50
Purchase #4	$104.91	4.773%	$109.9174	$109.92	$109.90	$109.90
Purchase #5	$38.57	13.504%	$43.7785	$43.78	$43.80	$43.80
Purchase #6	$29.37	8.166%	$31.7684	$31.77	$31.75	$31.80
Purchase #7	$193.86	8.429%	$210.2005	$210.20	$210.20	$210.20
7 purchase totals =	$745.78		$812.0183	$812.03	$812.00	$812.00