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	$34.93	6.472%	$37.1907	$37.19	$37.20	$37.20
Purchase #2	$227.54	8.293%	$246.4099	$246.41	$246.40	$246.40
Purchase #3	$79.34	12.261%	$89.0679	$89.07	$89.05	$89.10
Purchase #4	$47.41	10.581%	$52.4265	$52.43	$52.45	$52.40
Purchase #5	$71.41	7.725%	$76.9264	$76.93	$76.95	$76.90
Purchase #6	$31.58	12.605%	$35.5607	$35.56	$35.55	$35.60
Purchase #7	$174.89	6.168%	$185.6772	$185.68	$185.70	$185.70
7 purchase totals =	$667.10		$723.2593	$723.27	$723.30	$723.30