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	$81.65	10.239%	$90.0101	$90.01	$90.00	$90.00
Purchase #2	$133.50	12.668%	$150.4118	$150.41	$150.40	$150.40
Purchase #3	$191.43	13.121%	$216.5475	$216.55	$216.55	$216.50
Purchase #4	$18.81	13.734%	$21.3934	$21.39	$21.40	$21.40
Purchase #5	$120.46	3.394%	$124.5484	$124.55	$124.55	$124.50
Purchase #6	$130.92	4.570%	$136.903	$136.90	$136.90	$136.90
Purchase #7	$50.78	5.598%	$53.6227	$53.62	$53.60	$53.60
7 purchase totals =	$727.55		$793.4369	$793.43	$793.40	$793.30