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	$78.55	13.764%	$89.3616	$89.36	$89.35	$89.40
Purchase #2	$98.90	4.690%	$103.5384	$103.54	$103.55	$103.50
Purchase #3	$199.55	3.709%	$206.9513	$206.95	$206.95	$207.00
Purchase #4	$21.50	7.453%	$23.1024	$23.10	$23.10	$23.10
Purchase #5	$234.70	10.562%	$259.489	$259.49	$259.50	$259.50
Purchase #6	$219.83	5.425%	$231.7558	$231.76	$231.75	$231.80
Purchase #7	$17.46	6.520%	$18.5984	$18.60	$18.60	$18.60
7 purchase totals =	$870.49		$932.7969	$932.80	$932.80	$932.90