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	$48.33	12.435%	$54.3398	$54.34	$54.35	$54.30
Purchase #2	$8.32	12.615%	$9.3696	$9.37	$9.35	$9.40
Purchase #3	$114.53	3.441%	$118.471	$118.47	$118.45	$118.50
Purchase #4	$201.26	5.740%	$212.8123	$212.81	$212.80	$212.80
Purchase #5	$38.60	10.128%	$42.5094	$42.51	$42.50	$42.50
Purchase #6	$174.36	7.207%	$186.9261	$186.93	$186.95	$186.90
Purchase #7	$37.73	13.666%	$42.8862	$42.89	$42.90	$42.90
7 purchase totals =	$623.13		$667.3144	$667.32	$667.30	$667.30