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	$71.96	8.518%	$78.0896	$78.09	$78.10	$78.10
Purchase #2	$207.78	3.605%	$215.2705	$215.27	$215.25	$215.30
Purchase #3	$166.34	13.370%	$188.5797	$188.58	$188.60	$188.60
Purchase #4	$67.84	10.463%	$74.9381	$74.94	$74.95	$74.90
Purchase #5	$213.68	6.837%	$228.2893	$228.29	$228.30	$228.30
Purchase #6	$79.59	12.595%	$89.6144	$89.61	$89.60	$89.60
Purchase #7	$60.53	3.345%	$62.5547	$62.55	$62.55	$62.60
7 purchase totals =	$867.72		$937.3363	$937.33	$937.35	$937.40