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	$25.33	12.184%	$28.4162	$28.42	$28.40	$28.40
Purchase #2	$68.72	4.728%	$71.9691	$71.97	$71.95	$72.00
Purchase #3	$19.63	9.368%	$21.4689	$21.47	$21.45	$21.50
Purchase #4	$131.89	3.482%	$136.4824	$136.48	$136.50	$136.50
Purchase #5	$77.46	5.555%	$81.7629	$81.76	$81.75	$81.80
Purchase #6	$25.28	9.267%	$27.6227	$27.62	$27.60	$27.60
Purchase #7	$107.53	3.790%	$111.6054	$111.61	$111.60	$111.60
7 purchase totals =	$455.84		$479.3276	$479.33	$479.25	$479.40