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	$109.30	13.264%	$123.7976	$123.80	$123.80	$123.80
Purchase #2	$79.78	6.602%	$85.0471	$85.05	$85.05	$85.00
Purchase #3	$54.77	11.411%	$61.0198	$61.02	$61.00	$61.00
Purchase #4	$197.89	13.107%	$223.8274	$223.83	$223.85	$223.80
Purchase #5	$96.55	4.324%	$100.7248	$100.72	$100.70	$100.70
Purchase #6	$97.30	10.619%	$107.6323	$107.63	$107.65	$107.60
Purchase #7	$38.83	6.397%	$41.314	$41.31	$41.30	$41.30
7 purchase totals =	$674.42		$743.3630	$743.36	$743.35	$743.20