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	$84.46	5.752%	$89.3181	$89.32	$89.30	$89.30
Purchase #2	$34.90	13.152%	$39.49	$39.49	$39.50	$39.50
Purchase #3	$236.84	6.627%	$252.5354	$252.54	$252.55	$252.50
Purchase #4	$90.76	7.285%	$97.3719	$97.37	$97.35	$97.40
Purchase #5	$102.30	7.172%	$109.637	$109.64	$109.65	$109.60
Purchase #6	$88.64	6.825%	$94.6897	$94.69	$94.70	$94.70
Purchase #7	$133.99	9.358%	$146.5288	$146.53	$146.55	$146.50
7 purchase totals =	$771.89		$829.5709	$829.58	$829.60	$829.50