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	$82.95	9.860%	$91.1289	$91.13	$91.15	$91.10
Purchase #2	$230.79	8.691%	$250.848	$250.85	$250.85	$250.80
Purchase #3	$111.45	8.346%	$120.7516	$120.75	$120.75	$120.80
Purchase #4	$89.93	3.230%	$92.8347	$92.83	$92.85	$92.80
Purchase #5	$188.41	6.540%	$200.732	$200.73	$200.75	$200.70
Purchase #6	$203.96	13.520%	$231.5354	$231.54	$231.55	$231.50
Purchase #7	$118.83	7.400%	$127.6234	$127.62	$127.60	$127.60
7 purchase totals =	$1,026.32		$1,115.4540	$1,115.45	$1,115.50	$1,115.30