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	$72.56	10.836%	$80.4226	$80.42	$80.40	$80.40
Purchase #2	$168.99	12.527%	$190.1594	$190.16	$190.15	$190.20
Purchase #3	$31.27	8.446%	$33.9111	$33.91	$33.90	$33.90
Purchase #4	$177.93	12.130%	$199.5129	$199.51	$199.50	$199.50
Purchase #5	$12.31	6.794%	$13.1463	$13.15	$13.15	$13.10
Purchase #6	$29.31	6.385%	$31.1814	$31.18	$31.20	$31.20
Purchase #7	$232.96	11.646%	$260.0905	$260.09	$260.10	$260.10
7 purchase totals =	$725.33		$808.4242	$808.42	$808.40	$808.40