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	$33.30	11.488%	$37.1255	$37.13	$37.15	$37.10
Purchase #2	$226.61	8.497%	$245.8651	$245.87	$245.85	$245.90
Purchase #3	$200.78	12.505%	$225.8875	$225.89	$225.90	$225.90
Purchase #4	$202.37	5.797%	$214.1014	$214.10	$214.10	$214.10
Purchase #5	$40.76	11.847%	$45.5888	$45.59	$45.60	$45.60
Purchase #6	$248.85	12.770%	$280.6281	$280.63	$280.65	$280.60
Purchase #7	$146.77	6.190%	$155.8551	$155.86	$155.85	$155.90
7 purchase totals =	$1,099.44		$1,205.0515	$1,205.07	$1,205.10	$1,205.10