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	$137.77	12.523%	$155.0229	$155.02	$155.00	$155.00
Purchase #2	$33.27	13.472%	$37.7521	$37.75	$37.75	$37.80
Purchase #3	$75.51	12.745%	$85.1337	$85.13	$85.15	$85.10
Purchase #4	$147.69	11.408%	$164.5385	$164.54	$164.55	$164.50
Purchase #5	$187.57	8.441%	$203.4028	$203.40	$203.40	$203.40
Purchase #6	$91.51	5.341%	$96.3975	$96.40	$96.40	$96.40
Purchase #7	$61.60	4.501%	$64.3726	$64.37	$64.35	$64.40
7 purchase totals =	$734.92		$806.6201	$806.61	$806.60	$806.60