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	$77.92	3.157%	$80.3799	$80.38	$80.40	$80.40
Purchase #2	$150.41	6.307%	$159.8964	$159.90	$159.90	$159.90
Purchase #3	$46.29	11.213%	$51.4805	$51.48	$51.50	$51.50
Purchase #4	$174.37	13.780%	$198.3982	$198.40	$198.40	$198.40
Purchase #5	$52.59	3.118%	$54.2298	$54.23	$54.25	$54.20
Purchase #6	$65.35	7.785%	$70.4375	$70.44	$70.45	$70.40
Purchase #7	$172.76	5.709%	$182.6229	$182.62	$182.60	$182.60
7 purchase totals =	$739.69		$797.4452	$797.45	$797.50	$797.40