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	$38.51	5.512%	$40.6327	$40.63	$40.65	$40.60
Purchase #2	$63.51	3.869%	$65.9672	$65.97	$65.95	$66.00
Purchase #3	$182.93	3.602%	$189.5191	$189.52	$189.50	$189.50
Purchase #4	$156.29	11.671%	$174.5306	$174.53	$174.55	$174.50
Purchase #5	$125.60	10.203%	$138.415	$138.42	$138.40	$138.40
Purchase #6	$97.69	12.129%	$109.5388	$109.54	$109.55	$109.50
Purchase #7	$170.86	8.576%	$185.513	$185.51	$185.50	$185.50
7 purchase totals =	$835.39		$904.1164	$904.12	$904.10	$904.00