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	$37.61	13.565%	$42.7118	$42.71	$42.70	$42.70
Purchase #2	$241.46	9.627%	$264.7054	$264.71	$264.70	$264.70
Purchase #3	$170.56	9.264%	$186.3607	$186.36	$186.35	$186.40
Purchase #4	$213.46	11.655%	$238.3388	$238.34	$238.35	$238.30
Purchase #5	$222.27	8.762%	$241.7453	$241.75	$241.75	$241.70
Purchase #6	$65.54	3.164%	$67.6137	$67.61	$67.60	$67.60
Purchase #7	$230.51	9.143%	$251.5855	$251.59	$251.60	$251.60
7 purchase totals =	$1,181.41		$1,293.0612	$1,293.07	$1,293.05	$1,293.00