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	$30.28	7.397%	$32.5198	$32.52	$32.50	$32.50
Purchase #2	$195.81	7.145%	$209.8006	$209.80	$209.80	$209.80
Purchase #3	$250.54	5.124%	$263.3777	$263.38	$263.40	$263.40
Purchase #4	$234.93	4.561%	$245.6452	$245.65	$245.65	$245.60
Purchase #5	$46.89	9.689%	$51.4332	$51.43	$51.45	$51.40
Purchase #6	$164.65	6.800%	$175.8462	$175.85	$175.85	$175.80
Purchase #7	$55.98	9.437%	$61.2628	$61.26	$61.25	$61.30
7 purchase totals =	$979.08		$1,039.8855	$1,039.89	$1,039.90	$1,039.80