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	$212.31	9.498%	$232.4752	$232.48	$232.50	$232.50
Purchase #2	$77.71	5.864%	$82.2669	$82.27	$82.25	$82.30
Purchase #3	$18.56	13.331%	$21.0342	$21.03	$21.05	$21.00
Purchase #4	$112.90	10.147%	$124.356	$124.36	$124.35	$124.40
Purchase #5	$129.25	10.266%	$142.5188	$142.52	$142.50	$142.50
Purchase #6	$106.49	7.467%	$114.4416	$114.44	$114.45	$114.40
Purchase #7	$248.69	12.347%	$279.3958	$279.40	$279.40	$279.40
7 purchase totals =	$905.91		$996.4885	$996.50	$996.50	$996.50