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	$186.27	6.593%	$198.5508	$198.55	$198.55	$198.60
Purchase #2	$102.95	10.326%	$113.5806	$113.58	$113.60	$113.60
Purchase #3	$206.91	11.838%	$231.404	$231.40	$231.40	$231.40
Purchase #4	$12.26	13.483%	$13.913	$13.91	$13.90	$13.90
Purchase #5	$30.38	8.485%	$32.9577	$32.96	$32.95	$33.00
Purchase #6	$169.46	6.111%	$179.8157	$179.82	$179.80	$179.80
Purchase #7	$57.37	3.845%	$59.5759	$59.58	$59.60	$59.60
7 purchase totals =	$765.60		$829.7977	$829.80	$829.80	$829.90