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	$19.72	7.836%	$21.2653	$21.27	$21.25	$21.30
Purchase #2	$46.50	10.757%	$51.502	$51.50	$51.50	$51.50
Purchase #3	$63.60	6.304%	$67.6093	$67.61	$67.60	$67.60
Purchase #4	$239.88	4.837%	$251.483	$251.48	$251.50	$251.50
Purchase #5	$30.37	3.642%	$31.4761	$31.48	$31.50	$31.50
Purchase #6	$169.31	9.342%	$185.1269	$185.13	$185.15	$185.10
Purchase #7	$230.35	4.575%	$240.8885	$240.89	$240.90	$240.90
7 purchase totals =	$799.73		$849.3511	$849.36	$849.40	$849.40