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	$136.82	10.835%	$151.6444	$151.64	$151.65	$151.60
Purchase #2	$94.47	9.586%	$103.5259	$103.53	$103.55	$103.50
Purchase #3	$250.63	8.812%	$272.7155	$272.72	$272.70	$272.70
Purchase #4	$149.27	13.188%	$168.9557	$168.96	$168.95	$169.00
Purchase #5	$147.50	5.869%	$156.1568	$156.16	$156.15	$156.20
Purchase #6	$164.33	12.579%	$185.0011	$185.00	$185.00	$185.00
Purchase #7	$10.81	9.603%	$11.8481	$11.85	$11.85	$11.80
7 purchase totals =	$953.83		$1,049.8475	$1,049.86	$1,049.85	$1,049.80