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	$122.53	9.299%	$133.9241	$133.92	$133.90	$133.90
Purchase #2	$7.65	3.438%	$7.913	$7.91	$7.90	$7.90
Purchase #3	$113.94	6.368%	$121.1957	$121.20	$121.20	$121.20
Purchase #4	$101.33	6.503%	$107.9195	$107.92	$107.90	$107.90
Purchase #5	$55.87	6.617%	$59.5669	$59.57	$59.55	$59.60
Purchase #6	$37.61	13.829%	$42.8111	$42.81	$42.80	$42.80
Purchase #7	$34.29	8.471%	$37.1947	$37.19	$37.20	$37.20
7 purchase totals =	$473.22		$510.5250	$510.52	$510.45	$510.50