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	$13.79	12.677%	$15.5382	$15.54	$15.55	$15.50
Purchase #2	$35.72	9.123%	$38.9787	$38.98	$39.00	$39.00
Purchase #3	$179.71	11.598%	$200.5528	$200.55	$200.55	$200.60
Purchase #4	$58.54	7.583%	$62.9791	$62.98	$63.00	$63.00
Purchase #5	$206.53	12.234%	$231.7969	$231.80	$231.80	$231.80
Purchase #6	$172.41	6.672%	$183.9132	$183.91	$183.90	$183.90
Purchase #7	$111.61	6.238%	$118.5722	$118.57	$118.55	$118.60
7 purchase totals =	$778.31		$852.3311	$852.33	$852.35	$852.40