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	$125.29	7.748%	$134.9975	$135.00	$135.00	$135.00
Purchase #2	$71.55	10.253%	$78.886	$78.89	$78.90	$78.90
Purchase #3	$95.67	4.536%	$100.0096	$100.01	$100.00	$100.00
Purchase #4	$203.69	9.542%	$223.1261	$223.13	$223.15	$223.10
Purchase #5	$48.64	9.814%	$53.4135	$53.41	$53.40	$53.40
Purchase #6	$50.42	8.102%	$54.505	$54.51	$54.50	$54.50
Purchase #7	$194.64	12.293%	$218.5671	$218.57	$218.55	$218.60
7 purchase totals =	$789.90		$863.5048	$863.52	$863.50	$863.50