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	$64.85	13.327%	$73.4926	$73.49	$73.50	$73.50
Purchase #2	$39.53	8.806%	$43.011	$43.01	$43.00	$43.00
Purchase #3	$222.63	11.826%	$248.9582	$248.96	$248.95	$249.00
Purchase #4	$38.54	12.751%	$43.4542	$43.45	$43.45	$43.50
Purchase #5	$136.69	8.746%	$148.6449	$148.64	$148.65	$148.60
Purchase #6	$35.72	3.536%	$36.9831	$36.98	$37.00	$37.00
Purchase #7	$137.63	9.273%	$150.3924	$150.39	$150.40	$150.40
7 purchase totals =	$675.59		$744.9364	$744.92	$744.95	$745.00