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	$245.51	3.872%	$255.0161	$255.02	$255.00	$255.00
Purchase #2	$225.57	6.851%	$241.0238	$241.02	$241.00	$241.00
Purchase #3	$104.96	6.339%	$111.6134	$111.61	$111.60	$111.60
Purchase #4	$133.95	12.576%	$150.7956	$150.80	$150.80	$150.80
Purchase #5	$122.38	11.803%	$136.8245	$136.82	$136.80	$136.80
Purchase #6	$191.87	7.735%	$206.7111	$206.71	$206.70	$206.70
Purchase #7	$35.32	12.553%	$39.7537	$39.75	$39.75	$39.80
7 purchase totals =	$1,059.56		$1,141.7382	$1,141.73	$1,141.65	$1,141.70