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	$82.54	10.328%	$91.0647	$91.06	$91.05	$91.10
Purchase #2	$78.78	13.110%	$89.1081	$89.11	$89.10	$89.10
Purchase #3	$233.70	11.172%	$259.809	$259.81	$259.80	$259.80
Purchase #4	$198.42	7.675%	$213.6487	$213.65	$213.65	$213.60
Purchase #5	$122.76	8.241%	$132.8767	$132.88	$132.90	$132.90
Purchase #6	$114.27	13.611%	$129.8233	$129.82	$129.80	$129.80
Purchase #7	$41.39	4.162%	$43.1127	$43.11	$43.10	$43.10
7 purchase totals =	$871.86		$959.4432	$959.44	$959.40	$959.40