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	$147.36	13.426%	$167.1446	$167.14	$167.15	$167.10
Purchase #2	$82.89	9.730%	$90.9552	$90.96	$90.95	$91.00
Purchase #3	$143.51	7.658%	$154.5	$154.50	$154.50	$154.50
Purchase #4	$226.34	8.215%	$244.9338	$244.93	$244.95	$244.90
Purchase #5	$92.76	13.139%	$104.9477	$104.95	$104.95	$104.90
Purchase #6	$123.60	10.587%	$136.6855	$136.69	$136.70	$136.70
Purchase #7	$56.29	5.659%	$59.4755	$59.48	$59.50	$59.50
7 purchase totals =	$872.75		$958.6423	$958.65	$958.70	$958.60