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	$40.59	3.744%	$42.1097	$42.11	$42.10	$42.10
Purchase #2	$245.72	11.704%	$274.4791	$274.48	$274.50	$274.50
Purchase #3	$81.47	8.391%	$88.3061	$88.31	$88.30	$88.30
Purchase #4	$114.88	7.182%	$123.1307	$123.13	$123.15	$123.10
Purchase #5	$102.84	5.660%	$108.6607	$108.66	$108.65	$108.70
Purchase #6	$46.58	8.353%	$50.4708	$50.47	$50.45	$50.50
Purchase #7	$177.82	8.837%	$193.534	$193.53	$193.55	$193.50
7 purchase totals =	$809.90		$880.6911	$880.69	$880.70	$880.70