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	$206.50	9.552%	$226.2249	$226.22	$226.20	$226.20
Purchase #2	$86.26	13.136%	$97.5911	$97.59	$97.60	$97.60
Purchase #3	$79.38	3.717%	$82.3306	$82.33	$82.35	$82.30
Purchase #4	$89.84	10.870%	$99.6056	$99.61	$99.60	$99.60
Purchase #5	$50.87	11.525%	$56.7328	$56.73	$56.75	$56.70
Purchase #6	$113.43	8.619%	$123.2065	$123.21	$123.20	$123.20
Purchase #7	$87.62	9.669%	$96.092	$96.09	$96.10	$96.10
7 purchase totals =	$713.90		$781.7835	$781.78	$781.80	$781.70