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	$82.53	9.533%	$90.3976	$90.40	$90.40	$90.40
Purchase #2	$246.55	6.294%	$262.0679	$262.07	$262.05	$262.10
Purchase #3	$199.62	12.724%	$225.0196	$225.02	$225.00	$225.00
Purchase #4	$98.79	9.134%	$107.8135	$107.81	$107.80	$107.80
Purchase #5	$215.89	11.574%	$240.8771	$240.88	$240.90	$240.90
Purchase #6	$47.72	11.816%	$53.3586	$53.36	$53.35	$53.40
Purchase #7	$124.33	13.530%	$141.1518	$141.15	$141.15	$141.20
7 purchase totals =	$1,015.43		$1,120.6861	$1,120.69	$1,120.65	$1,120.80