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	$243.33	8.498%	$264.0082	$264.01	$264.00	$264.00
Purchase #2	$84.83	5.660%	$89.6314	$89.63	$89.65	$89.60
Purchase #3	$11.87	13.429%	$13.464	$13.46	$13.45	$13.50
Purchase #4	$25.96	13.349%	$29.4254	$29.43	$29.45	$29.40
Purchase #5	$133.50	4.598%	$139.6383	$139.64	$139.65	$139.60
Purchase #6	$7.88	8.463%	$8.5469	$8.55	$8.55	$8.50
Purchase #7	$224.27	13.401%	$254.3244	$254.32	$254.30	$254.30
7 purchase totals =	$731.64		$799.0386	$799.04	$799.05	$798.90