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	$69.34	12.630%	$78.0976	$78.10	$78.10	$78.10
Purchase #2	$199.30	11.715%	$222.648	$222.65	$222.65	$222.60
Purchase #3	$34.49	13.873%	$39.2748	$39.27	$39.25	$39.30
Purchase #4	$68.59	3.709%	$71.134	$71.13	$71.15	$71.10
Purchase #5	$85.60	9.343%	$93.5976	$93.60	$93.60	$93.60
Purchase #6	$242.95	6.717%	$259.269	$259.27	$259.25	$259.30
Purchase #7	$231.34	11.340%	$257.574	$257.57	$257.55	$257.60
7 purchase totals =	$931.61		$1,021.5950	$1,021.59	$1,021.55	$1,021.60