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	$83.92	6.503%	$89.3773	$89.38	$89.40	$89.40
Purchase #2	$209.47	13.457%	$237.6584	$237.66	$237.65	$237.70
Purchase #3	$87.85	9.344%	$96.0587	$96.06	$96.05	$96.10
Purchase #4	$141.72	10.338%	$156.371	$156.37	$156.35	$156.40
Purchase #5	$161.76	7.813%	$174.3983	$174.40	$174.40	$174.40
Purchase #6	$64.60	4.524%	$67.5225	$67.52	$67.50	$67.50
Purchase #7	$43.35	5.384%	$45.684	$45.68	$45.70	$45.70
7 purchase totals =	$792.67		$867.0702	$867.07	$867.05	$867.20