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	$76.51	3.172%	$78.9369	$78.94	$78.95	$78.90
Purchase #2	$89.96	5.647%	$95.04	$95.04	$95.05	$95.00
Purchase #3	$158.74	3.799%	$164.7705	$164.77	$164.75	$164.80
Purchase #4	$28.67	13.452%	$32.5267	$32.53	$32.55	$32.50
Purchase #5	$144.77	13.801%	$164.7497	$164.75	$164.75	$164.70
Purchase #6	$96.90	4.513%	$101.2731	$101.27	$101.25	$101.30
Purchase #7	$172.99	11.310%	$192.5552	$192.56	$192.55	$192.60
7 purchase totals =	$768.54		$829.8521	$829.86	$829.85	$829.80