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	$27.68	10.488%	$30.5831	$30.58	$30.60	$30.60
Purchase #2	$172.97	13.860%	$196.9436	$196.94	$196.95	$196.90
Purchase #3	$147.97	13.494%	$167.9371	$167.94	$167.95	$167.90
Purchase #4	$211.71	9.173%	$231.1302	$231.13	$231.15	$231.10
Purchase #5	$69.78	5.481%	$73.6046	$73.60	$73.60	$73.60
Purchase #6	$78.96	8.316%	$85.5263	$85.53	$85.55	$85.50
Purchase #7	$144.35	5.343%	$152.0626	$152.06	$152.05	$152.10
7 purchase totals =	$853.42		$937.7875	$937.78	$937.85	$937.70