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	$156.57	4.805%	$164.0932	$164.09	$164.10	$164.10
Purchase #2	$102.89	9.707%	$112.8775	$112.88	$112.90	$112.90
Purchase #3	$63.47	11.564%	$70.8097	$70.81	$70.80	$70.80
Purchase #4	$106.66	9.767%	$117.0775	$117.08	$117.10	$117.10
Purchase #5	$238.57	9.199%	$260.5161	$260.52	$260.50	$260.50
Purchase #6	$181.56	3.294%	$187.5406	$187.54	$187.55	$187.50
Purchase #7	$161.82	7.361%	$173.7316	$173.73	$173.75	$173.70
7 purchase totals =	$1,011.54		$1,086.6462	$1,086.65	$1,086.70	$1,086.60