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	$6.67	4.586%	$6.9759	$6.98	$7.00	$7.00
Purchase #2	$234.40	8.167%	$253.5434	$253.54	$253.55	$253.50
Purchase #3	$174.44	5.788%	$184.5366	$184.54	$184.55	$184.50
Purchase #4	$33.94	9.200%	$37.0625	$37.06	$37.05	$37.10
Purchase #5	$69.56	11.272%	$77.4008	$77.40	$77.40	$77.40
Purchase #6	$166.40	12.702%	$187.5361	$187.54	$187.55	$187.50
Purchase #7	$184.93	6.413%	$196.7896	$196.79	$196.80	$196.80
7 purchase totals =	$870.34		$943.8449	$943.85	$943.90	$943.80