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	$14.83	13.763%	$16.8711	$16.87	$16.85	$16.90
Purchase #2	$199.44	8.456%	$216.3046	$216.30	$216.30	$216.30
Purchase #3	$209.63	10.274%	$231.1674	$231.17	$231.15	$231.20
Purchase #4	$78.36	5.406%	$82.5961	$82.60	$82.60	$82.60
Purchase #5	$130.28	9.537%	$142.7048	$142.70	$142.70	$142.70
Purchase #6	$75.87	6.112%	$80.5072	$80.51	$80.50	$80.50
Purchase #7	$90.92	10.259%	$100.2475	$100.25	$100.25	$100.20
7 purchase totals =	$799.33		$870.3987	$870.40	$870.35	$870.40