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	$134.66	5.244%	$141.7216	$141.72	$141.70	$141.70
Purchase #2	$91.94	4.577%	$96.1481	$96.15	$96.15	$96.10
Purchase #3	$19.43	10.526%	$21.4752	$21.48	$21.50	$21.50
Purchase #4	$189.48	4.710%	$198.4045	$198.40	$198.40	$198.40
Purchase #5	$49.39	7.177%	$52.9347	$52.93	$52.95	$52.90
Purchase #6	$115.66	13.871%	$131.7032	$131.70	$131.70	$131.70
Purchase #7	$164.42	10.741%	$182.0804	$182.08	$182.10	$182.10
7 purchase totals =	$764.98		$824.4677	$824.46	$824.50	$824.40