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	$220.35	3.674%	$228.4457	$228.45	$228.45	$228.40
Purchase #2	$17.70	4.202%	$18.4438	$18.44	$18.45	$18.40
Purchase #3	$42.67	8.685%	$46.3759	$46.38	$46.40	$46.40
Purchase #4	$59.67	6.279%	$63.4167	$63.42	$63.40	$63.40
Purchase #5	$181.55	4.381%	$189.5037	$189.50	$189.50	$189.50
Purchase #6	$59.52	3.562%	$61.6401	$61.64	$61.65	$61.60
Purchase #7	$62.52	7.256%	$67.0565	$67.06	$67.05	$67.10
7 purchase totals =	$643.98		$674.8824	$674.89	$674.90	$674.80