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	$86.32	5.171%	$90.7836	$90.78	$90.80	$90.80
Purchase #2	$159.79	7.248%	$171.3716	$171.37	$171.35	$171.40
Purchase #3	$116.90	7.228%	$125.3495	$125.35	$125.35	$125.30
Purchase #4	$165.31	5.373%	$174.1921	$174.19	$174.20	$174.20
Purchase #5	$56.63	12.510%	$63.7144	$63.71	$63.70	$63.70
Purchase #6	$101.94	9.322%	$111.4428	$111.44	$111.45	$111.40
Purchase #7	$50.52	6.797%	$53.9538	$53.95	$53.95	$54.00
7 purchase totals =	$737.41		$790.8078	$790.79	$790.80	$790.80