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	$6.65	10.723%	$7.3631	$7.36	$7.35	$7.40
Purchase #2	$236.42	11.467%	$263.5303	$263.53	$263.55	$263.50
Purchase #3	$89.34	11.854%	$99.9304	$99.93	$99.95	$99.90
Purchase #4	$216.57	10.300%	$238.8767	$238.88	$238.90	$238.90
Purchase #5	$102.46	9.310%	$111.999	$112.00	$112.00	$112.00
Purchase #6	$201.45	6.493%	$214.5301	$214.53	$214.55	$214.50
Purchase #7	$209.94	9.868%	$230.6569	$230.66	$230.65	$230.70
7 purchase totals =	$1,062.83		$1,166.8865	$1,166.89	$1,166.95	$1,166.90