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	$157.97	6.352%	$168.0043	$168.00	$168.00	$168.00
Purchase #2	$137.95	12.656%	$155.409	$155.41	$155.40	$155.40
Purchase #3	$195.49	13.242%	$221.3768	$221.38	$221.40	$221.40
Purchase #4	$221.73	10.191%	$244.3265	$244.33	$244.35	$244.30
Purchase #5	$28.37	9.868%	$31.1696	$31.17	$31.15	$31.20
Purchase #6	$54.97	7.388%	$59.0312	$59.03	$59.05	$59.00
Purchase #7	$54.97	13.504%	$62.3931	$62.39	$62.40	$62.40
7 purchase totals =	$851.45		$941.7105	$941.71	$941.75	$941.70