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	$209.27	4.107%	$217.8647	$217.86	$217.85	$217.90
Purchase #2	$181.48	9.363%	$198.472	$198.47	$198.45	$198.50
Purchase #3	$61.55	3.249%	$63.5498	$63.55	$63.55	$63.50
Purchase #4	$96.53	7.441%	$103.7128	$103.71	$103.70	$103.70
Purchase #5	$87.95	13.478%	$99.8039	$99.80	$99.80	$99.80
Purchase #6	$204.33	12.502%	$229.8753	$229.88	$229.90	$229.90
Purchase #7	$18.93	5.847%	$20.0368	$20.04	$20.05	$20.00
7 purchase totals =	$860.04		$933.3153	$933.31	$933.30	$933.30