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	$74.90	4.700%	$78.4203	$78.42	$78.40	$78.40
Purchase #2	$150.45	13.418%	$170.6374	$170.64	$170.65	$170.60
Purchase #3	$249.73	13.367%	$283.1114	$283.11	$283.10	$283.10
Purchase #4	$206.43	7.776%	$222.482	$222.48	$222.50	$222.50
Purchase #5	$203.89	10.113%	$224.5094	$224.51	$224.50	$224.50
Purchase #6	$53.46	3.748%	$55.4637	$55.46	$55.45	$55.50
Purchase #7	$82.29	9.837%	$90.3849	$90.38	$90.40	$90.40
7 purchase totals =	$1,021.15		$1,125.0091	$1,125.00	$1,125.00	$1,125.00