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	$87.46	3.223%	$90.2788	$90.28	$90.30	$90.30
Purchase #2	$39.67	8.715%	$43.1272	$43.13	$43.15	$43.10
Purchase #3	$55.45	3.705%	$57.5044	$57.50	$57.50	$57.50
Purchase #4	$52.44	3.840%	$54.4537	$54.45	$54.45	$54.50
Purchase #5	$189.77	9.310%	$207.4376	$207.44	$207.45	$207.40
Purchase #6	$15.88	5.223%	$16.7094	$16.71	$16.70	$16.70
Purchase #7	$188.63	5.800%	$199.5705	$199.57	$199.55	$199.60
7 purchase totals =	$629.30		$669.0816	$669.08	$669.10	$669.10