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	$113.38	6.434%	$120.6749	$120.67	$120.65	$120.70
Purchase #2	$179.48	3.429%	$185.6344	$185.63	$185.65	$185.60
Purchase #3	$111.99	8.790%	$121.8339	$121.83	$121.85	$121.80
Purchase #4	$16.53	12.441%	$18.5865	$18.59	$18.60	$18.60
Purchase #5	$85.45	12.253%	$95.9202	$95.92	$95.90	$95.90
Purchase #6	$71.73	9.585%	$78.6053	$78.61	$78.60	$78.60
Purchase #7	$211.80	10.305%	$233.626	$233.63	$233.65	$233.60
7 purchase totals =	$790.36		$854.8812	$854.88	$854.90	$854.80