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	$100.27	11.700%	$112.0016	$112.00	$112.00	$112.00
Purchase #2	$242.37	8.673%	$263.3908	$263.39	$263.40	$263.40
Purchase #3	$149.41	13.628%	$169.7716	$169.77	$169.75	$169.80
Purchase #4	$150.67	6.738%	$160.8221	$160.82	$160.80	$160.80
Purchase #5	$22.75	12.296%	$25.5473	$25.55	$25.55	$25.50
Purchase #6	$96.98	3.864%	$100.7273	$100.73	$100.75	$100.70
Purchase #7	$137.31	4.114%	$142.9589	$142.96	$142.95	$143.00
7 purchase totals =	$899.76		$975.2196	$975.22	$975.20	$975.20