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	$17.59	4.807%	$18.4356	$18.44	$18.45	$18.40
Purchase #2	$11.95	9.544%	$13.0905	$13.09	$13.10	$13.10
Purchase #3	$185.54	11.445%	$206.7751	$206.78	$206.80	$206.80
Purchase #4	$29.99	11.184%	$33.3441	$33.34	$33.35	$33.30
Purchase #5	$69.54	3.759%	$72.154	$72.15	$72.15	$72.20
Purchase #6	$79.27	12.674%	$89.3167	$89.32	$89.30	$89.30
Purchase #7	$84.38	3.315%	$87.1772	$87.18	$87.20	$87.20
7 purchase totals =	$478.26		$520.2932	$520.30	$520.35	$520.30