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	$89.93	7.432%	$96.6136	$96.61	$96.60	$96.60
Purchase #2	$201.87	9.732%	$221.516	$221.52	$221.50	$221.50
Purchase #3	$128.67	9.164%	$140.4613	$140.46	$140.45	$140.50
Purchase #4	$46.95	9.113%	$51.2286	$51.23	$51.25	$51.20
Purchase #5	$89.87	4.798%	$94.182	$94.18	$94.20	$94.20
Purchase #6	$168.59	13.262%	$190.9484	$190.95	$190.95	$190.90
Purchase #7	$39.92	3.497%	$41.316	$41.32	$41.30	$41.30
7 purchase totals =	$765.80		$836.2659	$836.27	$836.25	$836.20