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	$112.93	13.496%	$128.171	$128.17	$128.15	$128.20
Purchase #2	$72.54	7.597%	$78.0509	$78.05	$78.05	$78.10
Purchase #3	$40.40	6.564%	$43.0519	$43.05	$43.05	$43.10
Purchase #4	$137.29	13.333%	$155.5949	$155.59	$155.60	$155.60
Purchase #5	$124.81	5.173%	$131.2664	$131.27	$131.25	$131.30
Purchase #6	$140.72	9.781%	$154.4838	$154.48	$154.50	$154.50
Purchase #7	$213.92	9.118%	$233.4252	$233.43	$233.45	$233.40
7 purchase totals =	$842.61		$924.0441	$924.04	$924.05	$924.20