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	$33.38	11.771%	$37.3092	$37.31	$37.30	$37.30
Purchase #2	$138.27	11.826%	$154.6218	$154.62	$154.60	$154.60
Purchase #3	$43.32	11.758%	$48.4136	$48.41	$48.40	$48.40
Purchase #4	$90.95	8.331%	$98.527	$98.53	$98.55	$98.50
Purchase #5	$208.29	10.218%	$229.5731	$229.57	$229.55	$229.60
Purchase #6	$133.29	7.228%	$142.9242	$142.92	$142.90	$142.90
Purchase #7	$183.45	12.415%	$206.2253	$206.23	$206.25	$206.20
7 purchase totals =	$830.95		$917.5942	$917.59	$917.55	$917.50