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	$100.89	4.116%	$105.0426	$105.04	$105.05	$105.00
Purchase #2	$189.90	8.197%	$205.4661	$205.47	$205.45	$205.50
Purchase #3	$242.66	3.561%	$251.3011	$251.30	$251.30	$251.30
Purchase #4	$106.70	5.256%	$112.3082	$112.31	$112.30	$112.30
Purchase #5	$14.89	9.391%	$16.2883	$16.29	$16.30	$16.30
Purchase #6	$143.25	6.502%	$152.5641	$152.56	$152.55	$152.60
Purchase #7	$25.96	6.104%	$27.5446	$27.54	$27.55	$27.50
7 purchase totals =	$824.25		$870.5150	$870.51	$870.50	$870.50