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	$131.73	6.409%	$140.1726	$140.17	$140.15	$140.20
Purchase #2	$78.95	5.623%	$83.3894	$83.39	$83.40	$83.40
Purchase #3	$194.56	7.240%	$208.6461	$208.65	$208.65	$208.60
Purchase #4	$47.97	6.174%	$50.9317	$50.93	$50.95	$50.90
Purchase #5	$181.74	8.320%	$196.8608	$196.86	$196.85	$196.90
Purchase #6	$235.39	4.767%	$246.611	$246.61	$246.60	$246.60
Purchase #7	$132.76	10.730%	$147.0051	$147.01	$147.00	$147.00
7 purchase totals =	$1,003.10		$1,073.6167	$1,073.62	$1,073.60	$1,073.60